Works in Progress Podcast

Saloni Dattani:
You would extract brain tissue from a rabid dog, inject it into the brains of rabbits.

Jacob Trefethen:
Frankenstein was written much earlier in the 19th century. You can sort of get why people had a view of scientists that was kind of like, "What the hell are they up to?"

Saloni Dattani:
He compiled all of it into his own manuscript, An Inquiry into the Causes and Effects of the Variolae Vaccinae.

Jacob Trefethen:
He submitted, got rejected, reviewer 2 had some comments, and then he became a Substacker?

Saloni Dattani:
Basically until the 1940s, you couldn't see the smallpox virus at all. And all of that changes when Ernst Ruska and Max Knoll developed the electron microscope. There's an enormous improvement in the resolution that you can get, thousands of times higher than light microscopy. And that finally allows you to see viruses.

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Saloni Dattani:
I think we have a few little announcements to make. So we have finally a print edition of Works in Progress magazine! And I'm holding it up right now, if you're watching the video, and it's very pretty, and if you haven't got one yet, you should get it. It's full of super interesting articles, including one about inflatable space stations.

Jacob Trefethen:
Inflatable space stations. At the time of the recording, Saloni's just arrived and mine has not, and I'm going to be checking my mailbox all day long. I can't wait for mine, and from what I've heard from you, Saloni, and others who were involved in the production of it, it's a beautiful piece in its own right just to flick through, so I definitely recommend others get a copy.

Saloni Dattani:
Yes. And then, you have some news.

Jacob Trefethen:
That is right. I work at Open Philanthropy, or I used to, because we just rebranded to Coefficient Giving to emphasize that we're going to work with more donors to give away more money to good causes. And what I work on is the kind of stuff we talk about in this podcast so science for global health and to make new vaccines and new drugs, and we are right now hiring on my team and on some other teams at Coefficient Giving. So I would recommend for anyone interested in these topics, or in philanthropy in general, to go ahead to coefficientgiving.org/about-us/careers or maybe just Google "Coefficient Giving careers" and then we list all of the open jobs that we have. I'd love to work with you one day maybe, so make sure to check it out.

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Jacob Trefethen:
According to the latest estimate in The Lancet, vaccines have saved 154 million lives over the last 50 years. Not bad, but where did they come from? How do you make a vaccine from scratch? How did scientists make the first vaccine and why did it take another 90 years to make a second one? What were all the challenges they faced along the way?

Saloni Dattani:
In this episode of Hard Drugs, we'll get into the mindset of a scientist living in the 18th century, then the 19th and the early 20th, trying to make vaccines for the first time with only limited tools and knowledge, and trying to find ways to make them safer, more effective, and scale them up.

Jacob Trefethen:
So, get into the time machine and let's begin. Okay, Saloni, we're going to try to get into the mindset of a scientist living in the 18th century to try and protect people against smallpox. Take me there.

Saloni Dattani:
So smallpox was really scary. I think it's easy for us to forget about that now because we've eradicated it. Just to first introduce what it was like.

Smallpox is caused by the Variola virus and you typically contract it if you inhale it, either through the air or through fluids and surfaces. The first thing that would happen is you would have fevers. You'd have fatigue and muscle pain, and then spots would start showing up on your tongue and your mouth. Then you'd have pimples and rashes all over your face, your chest, and all over your body.

All those pimples and the spots would then erupt. That would release new particles of the Variola virus into the air or into fluids, and then they could infect more people. While that's going on, the virus is replicating in your body, in your immune system, in your lungs, in your eyes, in your bones, in your heart. And that can cause a lot of problems.

Jacob Trefethen:
Your eyes and your bones?

Saloni Dattani:
It's horrible. Smallpox could cause blindness. It could cause arthritis. It could cause heart failure, sepsis, pneumonia. It's estimated that 30% of people who have any symptoms die from the disease. This is before any treatment, before vaccines are available.

Jacob Trefethen:
We have chickenpox and monkeypox still today, but they are poxes that create pustules. Not exactly as bad as 30% death rate, though.

Saloni Dattani:
That's right. Chickenpox is actually a totally different virus, but monkeypox is related to smallpox.

Trying to think of someone living in the 18th century, seeing this 30% death rate around them if there was a smallpox outbreak and someone caught it, and seeing that happen every year, every other year, that's terrifying, I think. You wouldn't really have the tools that we have today. You wouldn't know how the disease spread. You didn't know that it was caused by a virus. You didn't know what microbes were.

You wouldn't really have any idea of how to protect yourself, apart from staying away from other people, I guess. You wouldn't be able to see microbes- you wouldn't be able to see viruses under the microscope, certainly. You wouldn't be able to study the virus in the lab because you don't have the culture methods to do that.

All you would know is if there's a second epidemic in the same town, people who caught smallpox the first time would usually be protected from the second one. This was just this folk knowledge that people had of some kind of immunity. They didn't know why.

There were different kind of theories about this. One was that the first outbreak or the first time someone was infected with a disease, because you didn't really know what was caused by pathogens at that point, was that it somehow depleted the body of the nutrients that it needed. Then the second time it couldn't do the same thing.

Jacob Trefethen:
First cut is the deepest.

Saloni Dattani:
That's so good. You also wouldn't really have an understanding of contagion. Not the movie, the-

Jacob Trefethen:
Well, you wouldn't have an understanding of the movie either.

Saloni Dattani:
Right. Well, you would probably believe in miasma. You would think that diseases were spread through bad air, sometimes bad soil, just bad smells. Something around you in the environment is causing diseases to spread. And for a lot of diseases, that makes it quite hard to get rid of them. You're not really able to trace the disease very effectively, and you aren't able to develop vaccines with that. So, given all of that, how did Edward Jenner even develop the first vaccine? Do you know the answer?

Jacob Trefethen:
I think that he had spotted, or had read about, or heard anecdotally, that people who had been exposed to a related cowpox were more likely to be protected from smallpox. The milkmaids with clearer skin who had been working with cows, that kind of thing.

And I think there was also a part of the story I'm less sure about, which is that earlier in the 18th century, a British aristocrat or aristocratic woman, Lady Montagu, had been to the Ottoman Empire and seen how they were doing some vario- wherever she'd visited, they were doing variolation to protect against smallpox there and brought that back to the UK and did a big press tour about infecting her own child to protect her. It was safe, you could- I don't know if Edward Jenner was directly influenced by that background, but presumably so. I think he infected- he used the cowpox without, I guess, knowing it was a virus, but somehow exposing a young boy to it and then challenging him with a smallpox agent. And then the boy was okay! That's the story I have.

Saloni Dattani:
Mmhmm, so I think basically everything you said was correct. The lady that you're describing is Lady Mary Wortley Montagu, and she was an aristocrat. She traveled to the Ottoman Empire. She learned about Turkish customs and she witnessed people doing the smallpox inoculation, so she witnessed variolation at the time. Basically, they gave children a smaller, controlled dose of the virus. And she wrote about it in letters to her friends. Because she was so afraid that her children would have to go through the horrible disease, and one in three perhaps would not survive, she wanted to spare them. So she got her son inoculated, and he was the first English person in history to undergo this operation.

Jacob Trefethen:
So she didn't try it on herself?

Saloni Dattani:
Well, I guess she probably had had smallpox by that time, because it's mostly children who are having it for the first time. After that, she got her daughter inoculated by the doctor, and that time she publicized the event. She then persuaded the Princess of Wales at the time to also try it. She then got the prisoners at a prison to have the chance to undergo variolation instead of getting executed.

Jacob Trefethen:
Instead of getting executed? Those seem quite unrelated.

Saloni Dattani:
You know, variolation was still risky. I think that's something that we probably forget now. The estimate is that there was a 2% or so mortality rate from variolation.

Jacob Trefethen:
Two percent. Two percent? So you intentionally infect your child and there's 1 in 50 chance that your child then immediately dies?

Saloni Dattani:
Right. As a result of the procedure. I mean, I think that's freakishly scary to us now, but if you think about the alternative, which is smallpox, which is going to kill one in three, then the risk is much lower and it's very reasonable as a parent, but it's also just a terrible rite of passage that people would go through.

Jacob Trefethen:
This is the lesson that we always learn when we go back in a time machine, which is don't go back. Don't go back. Both options are very bad. Now I'm wondering, imagine if Lady Montagu had done a big show about variolating her daughter and then had hit the 2% chance and the daughter had just died? Would we even have vaccines now?

Saloni Dattani:
Oh... That's a really good point. I'm thankful that that didn't happen statistically, but it probably did for some of the early attempts. There were different procedures of how you could variolate someone at the time. One was you would get the pus from someone who had been infected, and then you would put that through another healthy child's nostril with a cotton, with a piece of cotton. Or with a thin silver tube, you would powder the pus and then blow it into their nostril. There were also different methods. You could use the fresh pus. You could cook the pox first and then put it into your nose.

Jacob Trefethen:
Cook the pox? Cook the pus?

Saloni Dattani:
Cook the pus, I think. But it was called cooked pox.

Jacob Trefethen:
Cooked pox. Well, that's a tasty little treat.

Saloni Dattani:
Yeah, recipe. What would you prefer?

Jacob Trefethen:
Oh my gosh. I want it as a cooked pox in a little sugar cube I can put in my cup of tea.

Saloni Dattani:
That's cute.

Jacob Trefethen:
Although I suppose I have to inhale it, don't I? So that wouldn't work. Okay. How about, I think I would do the blow it up your nose method. I think that just seems so kind of [whoosh] one and done. Moving on. What would you do?

Saloni Dattani:
I think I would... I would probably try to get the thing blown up my nose, but I think my nose is quite sensitive and I'd probably just sneeze it out.

Jacob Trefethen:
You'd sneeze it out and then two years later get smallpox.

Saloni Dattani:
Damn it.

Jacob Trefethen:
It's kind of interesting though that they had nasal vaccines back then and we can still barely invent nasal vaccines for respiratory viruses now.

Saloni Dattani:
That is true. The other thing that's interesting about the whole procedure was that variolation essentially involved putting actual smallpox virus into a child. You would try to guess based on the child who previously got it and that you're taking the pus from, whether they got this mild or severe disease. You just hope that that replicates and that there's a kind of uniform risk among different children and that some of those children are not just healthier and they're not just getting milder disease because of that. But you wouldn't be able to distinguish them because you didn't have the microscopy, you didn't have the culture techniques.

Jacob Trefethen:
Would doctors be harvesting from one child and passing it on to a hundred? Or would it be more like one to three?

Saloni Dattani:
I think you would be harvesting because you could collect- people would have so many pustules around their body that you could harvest multiple.

Jacob Trefethen:
I guess that gives you some chance of if you accidentally harvest the dangerous version, then you can just stop giving it after something bad happens.

Saloni Dattani:
Yep. You would have to make sure that you're actually recording all the details. Tallying up the numbers. I guess some doctors would have a reputation for accidentally killing lots of people and some would not.

Jacob Trefethen:
Not a good Yelp review.

Saloni Dattani:
This is also interesting because as we'll come back to with the smallpox vaccine, that was also transferred between people from arm to arm. But let's first start with how Jenner actually found that in the first place.

You described how he had heard rumors of dairy- of milkmaids being protected from smallpox after they'd had cowpox. That is right. What I learned while reading about this was that there were actually other doctors who tried it before Jenner did. They had actually also tried inoculating their children with cowpox. I think there are two doctors that we know of that have done this decades before Jenner.

But the key thing that Jenner did was actually write this up in a lot of detail and publicize it. I think sometimes that's really important. Just having the idea is not enough. You need to actually make it known and you need to be able to get other people to replicate this method and scale it up.

He had heard about these rumors and he went out into the dairy farms and he tried to find out more about it. He asked families, if there was a smallpox outbreak in the past, were any of your family members protected? Did they have cowpox before? He wrote up these case reports, dozens of case reports on people who had been protected. And then also experimented on one young boy, he inoculated a gardener's son called James Phipps, I think he was seven at the time, with pus from a cowpox infection by a woman named Sarah Nelmes, who was a dairymaid. Then in order to test whether that vaccine worked, he then variolated him with smallpox. It turned out he didn't have any symptoms after that.

This is the part of the story that I misunderstood at first. I thought that Jenner just gave him smallpox and tested that out. I thought that's really unethical. Maybe it was- maybe that's just how science was done at the time, but that's not actually what happened. He gave him variolation, which at that time would have been considered the safe option to do.

Jacob Trefethen:
Which reminds me of some vaccine development happening today, where in tuberculosis, it would not be safe to give someone a vaccine and then expose them to the tuberculosis bacteria because if the vaccine doesn't work, they're in trouble; the bacteria can be deadly.

But people are trying now to develop safer challenge models where you do give someone a vaccine and then expose them to something, so they're attenuating the bacteria. The issue, though, is that often the vaccines you're testing are attenuated bacteria, and then you're exposing someone to a challenge agent, which is attenuated bacteria. You're kind of giving people the same thing twice. But in this case, it sounds like there's one pox virus, cowpox, and then another virus.

Saloni Dattani:
Hopefully milder smallpox.

Jacob Trefethen:
Hopefully milder, yeah.

Saloni Dattani:
It's so funny that you're giving someone an attenuated bacterium to protect them from another attenuated bacterium. What if the second attenuated bacterium that's the challenge just happened to be so mild that the person wouldn't have had symptoms anyway?

Jacob Trefethen:
This is the difficulty from a scientific point of view of are you learning what you really want to learn? You've got to make it safer to learn anything, but you do get more distant from the reality of the bug.

Saloni Dattani:
Right. The other thing that I thought was quite interesting about the Jenner story was, he wrote up this experiment that he did on James Phipps and he submitted it to the Royal Society's academic journal, and they rejected him. They said, 'not sufficient evidence' in 1797. I guess he took some of their reviews- he took that comment to heart and he put together the other cases that he had described and compiled all of it into his own manuscript that he self-published as a monograph, which he titled An Inquiry into the Causes and Effects of the Variolae Vaccinae.

Jacob Trefethen:
He submitted, got rejected, reviewer 2 had some comments, which I'd love if those were public by the way, do you know if we can read- and then he became a Substacker?

Saloni Dattani:
This is so funny because even after he published his own version of the manuscript, people were still quite critical of it at the time. He still only had that one experiment, and he sort of mixed up the drawings a little bit, and people were like, "This isn't enough evidence." I just found that quite funny.

The way that he persuaded people was by continuing to do the experimenting and continuing to offer people the cowpox inoculation, and by people seeing that it works. More and more doctors would then ask him for the material and he would share it with them, and he kind of improved his manuscript and added more detail to it. I don't know, it's just interesting to me that all of this doesn't start with just one idea; it's this process that's building up over decades. And sometimes the key moment is not having the idea.

Jacob Trefethen:
That when we look back at- the stories of science end up condensing to this one eureka moment. But in fact, it's similar to science today, it just takes a long time, and a lot of people trying to disprove what you proposed.

Saloni Dattani:
Right. I guess I find it interesting that we sort of think often of experiments in history as, "oh, we just did this one experiment and then poof, everyone was convinced." Or maybe the opposite, it was like, "oh, they're so stupid they didn't believe him at first." But actually, people were just generally rigorous. It mattered whether this method worked. You wouldn't want to think that you'd protected your child and then actually they would die from another smallpox outbreak; that would be terrible. This stuff kind of mattered back then as well.

The other thing that I found interesting was just how different the vaccination method back then was to now. Once Jenner had developed his method, initially you would take a cowpox pustule and you would inoculate another child with it. How would you pass it on? You would either hope that there's a local outbreak of cowpox, which wasn't very common actually at the time, or there was this new method that people discovered, which was that you could transfer the pus from arm to arm. Once you had inoculated someone with a cowpox infection, you then remove the pus again from them and scratch it into another person. This is called arm-to-arm transfer.

And that worked, but it also kept dying out. So if you didn't have- the virus itself would die out from the person's arm or whatever you scratched it into them after a while. It was hard to actually spread it around the world and keep it around and keep it alive for long enough to vaccinate all the children.

I was reading about how this method got taken up in China at the time, and because the vaccine lineages just kept dying out, people in China, poorer families, were sometimes paid to get their children vaccinated just so that the vaccine didn't go extinct. It would be paid for by merchant guilds or local officials or shops or by taxation, just to make sure that we didn't accidentally get this extinct, because sometimes you wouldn't have another local cowpox outbreak to derive it again.

Jacob Trefethen:
I like the present day, where we have machines and bioreactors that keep things alive.

Saloni Dattani:
Right. We have big tanks with bacteria just churning out stuff that we want instead of scratching them from arm to arm. The other thing that I think you'll find interesting is that this process of transferring the pus from arm to arm, as you might be able to imagine, could also risk spreading other microbes between people. You could accidentally- you could have contamination. You could accidentally give someone syphilis or hepatitis B, and that happened often. I think that was quite scary for me to hear about.

Jacob Trefethen:
Oof, oof. Yeah, because you're breaking the skin and that means you're going to be- stuff might be getting straight into the bloodstream, right? Yeah, I'm not sure about that one.

Saloni Dattani:
Would you like a little side of syphilis with that?

Jacob Trefethen:
I think I will- No, I think I won't actually.

Saloni Dattani:
So the early smallpox vaccine was still quite risky. Obviously, it was a lot better than actual smallpox, and it was better than variolation. But there were still lots of improvements that had to be made for this to be a solution to vaccinate entire populations. I wonder if you can guess what the next step is.

Jacob Trefethen:
Well, first I have a question. So, getting smallpox, 30% mortality. Okay, don't want to do that. Variolation, say 2%. I mean, that is not good, I'm just going to be honest. Smallpox vaccination, this method with cowpox, how safe was it? Was it ever lethal? Would people, would kids actually go off the rails or?

Saloni Dattani:
I don't know that, I don't think there are numbers, but I do think we can be pretty confident that the risks are lower just because it's cowpox and cowpox is not very- it has a very low fatality rate. I don't think it actually caused fatalities at all. The only risks you would have are from contamination of syphilis or something else.

Jacob Trefethen:
Cool. Okay. Back to your question, was the question, how did they scale it up from here?

Saloni Dattani:
Or what was the next step after arm-to-arm transfer?

Jacob Trefethen:
After arm-to-arm, let's see. Well, I don't know if this fits into the story, but as I rack my brain for historical anecdotes, I remembered something about- oh no, this must have predated the vaccine. I was thinking of intentional exposure where there were sick kids who would cough in front of you, but that must have been before.

Saloni Dattani:
Oh, that might have been variolation. Or maybe you're thinking of chickenpox.

Jacob Trefethen:
That was just variolation. I was just thinking about it. Did you go to a chickenpox party, though?

Saloni Dattani:
I did not. It still makes me mad even today because the chickenpox vaccine was available when I was a kid, but my parents didn't get it for me, and I got actual chickenpox instead, and I was out for a week just throwing up. I remember this because I was maybe seven?

Jacob Trefethen:
Okay. You were James Phipps' age.

Saloni Dattani:
I was James Phipps' age, and I was in India on a holiday, and I was sick for a week. There was another little girl, my cousin's friend, was visiting. I was like, "you shouldn't come in here, I have chickenpox." Her mom said, "it's okay, she's had the chickenpox vaccine." I was like, "there's a chickenpox vaccine?"

Jacob Trefethen:
The reveal.

Saloni Dattani:
I was so mad. So where were we? What's the next step?

Jacob Trefethen:
Yes, what's the next step? You've got to somehow find a way to do this at scale instead of going arm to arm. Well, do they use cows? Why not? Cows are where the cowpox comes from.

Saloni Dattani:
You have, finally- you've got the right idea. That's exactly right. They moved to growing cowpox on cows. Quite strange. You're doing the arm-to-arm transfer, and then you're like, "What if we could just grow this on the skin of calves instead?" Yes. They're not actually getting cowpox, but well, they are on the skin.

This was a procedure that was developed by some doctors in Italy in the 1840s. At that time, it was obviously a lot safer because you're avoiding the other human pathogens that you could contaminate the vaccine with, so no risks of syphilis and hepatitis B anymore. But I think it took a few decades for that process to actually be passed on to other people because they didn't understand exactly how to do the method.

Jacob Trefethen:
That's multiple generations after Jenner.

Saloni Dattani:
Right. Until then, they're just doing this arm-to-arm transfer. There were kind of businesses that got set up that were called vaccine farms, and they would harvest the vaccine from these inoculated calves. I thought that was kind of interesting. They sort of handled this vaccine, the lymph or the pus, that was a biological material. I think it was also- this was the first time that there was a medical regulation on biological material in the US to regulate the quality of this smallpox vaccine and different vaccine farms.

Jacob Trefethen:
Hmm, what did that actually entail?

Saloni Dattani:
It was basically the general hygiene of the vaccine farms, but you don't want it to be contaminated with other stuff. Also, this is before antiseptic techniques are introduced or anything. It's literally just like, "oh, does this look clean? Looks good to me."

Jacob Trefethen:
I guess we don't have needles either, right? We have kind of scraping your skin with it.

Saloni Dattani:
Oh, no, we do have needles. We do have needles.

Jacob Trefethen:
We do have needles. I mean, one thing that came up in a previous episode was hepatitis C and how Egypt had a surprisingly high rate of hepatitis C. That was because in the 1970s, when we're 100 years of progress in medicine since what we're currently discussing, still needles were not properly sterilized, and there was a campaign to get rid of schistosomiasis in people who lived along the Nile. And you get-

Saloni Dattani:
Wait, what is schistosomiasis again?

Jacob Trefethen:
An infectious disease spread by snails, randomly.

Saloni Dattani:
Oh, that's horrible.

Jacob Trefethen:
Well, 'spread by' is not quite right. It's not that the snails sort of slide on top of you. The life cycle of the pathogen, which is a worm, involves a snail portion. That happens in water, so if you live by the Nile, you are kind of at risk. There was this big public health campaign to try and injecting people to treat schistosomiasis.

The issue being you needed 10+ injections and the needles weren't properly sterilized. Everyone got hepatitis C; not everyone, but fast forward- that generation of Egyptians, a lot of people were accidentally infected with hepatitis C, which was not discovered as a virus until 1989, so people didn't even know it was there. So now, the story ends happily because there are cures for hepatitis C. In Egypt, people got screened and treated, and the prevalence rate went from around 10% right down to, I think now, under 1%. But yeah-

Saloni Dattani:
Wow, that's horrible. I'm thinking, why didn't they just use disposable needles by default? Why not just use antiseptic techniques and things like that? Weird. Mistakes of the past.

Jacob Trefethen:
Mistakes of the past.

Saloni Dattani:
So, you've now got the smallpox vaccine that you can grow on cows. But there are still various things that you can do to scale that up. One is you could prevent it from spoiling quickly. You could add glycerin to it and do that. Then you can learn how to freeze dry the vaccine so you can transport it longer distances without losing its strength.

In the 1960s, there was also this other tool that was invented similar to the— well, not similar, but because you mentioned the needles, I remembered it- there were bifurcated needles, which are just two prongs on the needle, and they would hold a tiny drop of the vaccine in between them. And that meant that you could use only a quarter of the usual dose to get a standard dosage. That meant that you could scale up vaccination around the world.

Lots of progress that happened in the smallpox vaccine that I think is quite interesting, but it also just shows how very preliminary Edward Jenner's vaccine was and how little people understood. Throughout this whole process, basically until the 1940s, you couldn't see the smallpox virus at all. You just knew that something in this material is protecting people. You don't know what. You don't really know why. You just have this method that empirically works.

Jacob Trefethen:
Not much to work with there, then.

Saloni Dattani:
No. That really raises the question of how you can actually replicate, how do you do this for other diseases? I don't know if you have any guesses as to how the next step happened, but I think it's just interesting. Also, I think smallpox is kind of a rare case in that you just happen to have this milder version of the infection in cowpox.

Jacob Trefethen:
I was just thinking how lucky that was, because you don't get the next vaccine for so long. In order to replicate that model, you kind of would need there to be a related virus that happens to be mild.

Saloni Dattani:
Right, and that gives you protection.

Jacob Trefethen:
Yeah, exactly, that gives you cross-protection. What are cases where you can get cross-protection from something rather than having to try a different method of vaccine production?

Saloni Dattani:
There aren't really any, even now, there aren't really any, I think. So it just takes another 90 years to figure out how to do it.

Jacob Trefethen:
Well, let me try and come up with some on the fly. If I think about flus, there are some flus that would have been deadly back then and some flus that would have been mild. But I suppose those are more seasonal rather than ongoing, so it's hard. If you get a mild flu, you probably would get some cross-protection against some dangerous, lethal flus. But how do you keep that going? How do you know? Any others come to mind for you that?

Saloni Dattani:
I guess monkeypox and smallpox, but again, those are the same one. Is there cross-protection for hepatitis or syphilis or? No, that doesn't, that's really one strain.

Jacob Trefethen:
Well, there's meningitis B and gonorrhea. Both have an outer membrane vesicle. That might be some cross-protection. Gonorrhea is not deadly. Maybe you purposely infect yourself with that and get a little bit of protection against meningitis?

Saloni Dattani:
It would be hard to make the connection, I think.

Jacob Trefethen:
Yeah, no, that's true. I guess it helped not only that you had this milder case of cowpox, but also that smallpox was so common that you could determine the effect maybe, or you were motivated to determine the effect as well.

Saloni Dattani:
Also, it's quite easy to distinguish, or to tell, that someone has smallpox. It's so easy to tell that someone has cowpox and it's easy to get the pustules. If it was gonorrhea, maybe people just wouldn't tell you they would be so embarrassed or something and you wouldn't be able to replicate it.

Jacob Trefethen:
Well, okay, I've thought of one more.

Saloni Dattani:
Oh! Okay.

Jacob Trefethen:
Which is TB. Because, you know, the first vaccine is BCG, which is...

Saloni Dattani:
The cow version. It's bovine.

Jacob Trefethen:
The cow version. So how come they didn't come up with cow TB?

Saloni Dattani:
That's a really good question. I was wondering about this as well. The answer is they didn't know that they were different bacteria at the time. They didn't know that they were different strains.

Jacob Trefethen:
So they just thought.

Saloni Dattani:
So it wouldn't have worked. They would just be like, well, you're just infecting someone with TB.

Jacob Trefethen:
I see. There wasn't the equivalent because it's probably less visible. If you have TB, it's not the equivalent of cowpox. Interesting. I'm now wondering from the cow's point of view, if they look over at human smallpox and think it's puny and pathetic and they could have protected themselves against cowpox.

Saloni Dattani:
Right. Well, this is the other thing that's interesting, because smallpox doesn't infect other animals, right? It doesn't have any animal reservoirs. It just happens to be the case that cows get a similar but different infection.

Jacob Trefethen:
That's why to fast forward to the present, we managed to get rid of it. It doesn't hang around. If you're someone who wants to eradicate diseases, the first thing you should think about is "Which ones don't have an animal host? So I could actually..." I think syphilis-

Saloni Dattani:
Or you could vaccinate the animals.

Jacob Trefethen:
That's true. That's true. Bit harder, but doable.

Saloni Dattani:
Yes. Well, maybe a bit easier.

Jacob Trefethen:
It depends, yeah, I guess.

Saloni Dattani:
Can you catch them all?

Jacob Trefethen:
Gotta catch 'em all! We've eradicated two diseases, and one was a human disease and another- Do you know the other one?

Saloni Dattani:
I forgot. No, but it was a dairy farm one, wasn't it?

Jacob Trefethen:
Correct. Rinderpest.

Saloni Dattani:
Rinderpest!

Jacob Trefethen:
Rinderpest, which had a ridiculously high mortality rate for cows, where cows would start dying. You'd go, "what's going on?" You'd have an inspector come in and you'd go, "Oh, these cows have rinderpest." Then they'd walk out of the farm with some rinderpest on the bottom of their shoes and go to the next farm and spread it around. So these poor cows. But yeah, rinderpest, we managed to eradicate. Smallpox, we managed to eradicate for humans. We're one for one.

Saloni Dattani:
We're almost there for Guinea worm disease as well. Guinea worm is spread by a worm. It's a worm that you get from, I guess, swimming in stagnant lakes and things like that. Their eggs get into your body and they grow into very long worms, interfere with your joints and stuff like that, eventually they erupt from your skin and then you have to take them off and try not to let the worms lay more eggs in the water.

But we're almost there. I think in the last few years, there were only a dozen cases worldwide that were recorded versus hundreds of thousands, probably over a million, in the 1970s. It turns out it was extremely easy to eliminate that because you could just clean up the water or you could just introduce larvicides or something, to kill the worm's little eggs. I mean, this is totally off the point now, but I was reading about how Guinea worm unintentionally got eliminated in parts of Pakistan temporarily before the partition of India, just because there happened to be a drought. So all the eggs just died.

Jacob Trefethen:
Ooh. Wow.

Saloni Dattani:
Imagine that.

Jacob Trefethen:
Imagine that. It's like all the things during COVID, all the other respiratory diseases that dropped because no one was seeing each other anymore. I don't think we got rid of any, I mean, we almost got rid of flu B for a while.

Saloni Dattani:
We got rid of one strain of flu B, the Yamagata strain.

Jacob Trefethen:
Right. Is that just gone?

Saloni Dattani:
We haven't seen it in the last five years.

Jacob Trefethen:
Well, I've got a surprise for you...

Saloni Dattani:
No!!!

Jacob Trefethen:
Reveal! Let's get back on point. So what question did you ask me?

Saloni Dattani:
Okay. We've got the smallpox vaccine, improved it in a bunch of ways, scaled it up. Now we can store it for longer. We can use only a quarter of the usual dose. You can vaccinate basically everyone with it. The way that it was eradicated was by, if there were any cases that were remaining, people just vaccinated all of their contacts and everyone around them. That's called ring vaccination, so you just control the outbreak before it could spread anymore. Managed to eradicate that in 1980. Pretty cool.

Jacob Trefethen:
The people who did that are still alive today. Bill Foege. It was a team effort, so I don't want to single just him out, but I think he was the guy at the CDC at the time who was like, "Okay, we're just going to get rid of this thing." He's still alive!

Saloni Dattani:
He's still alive! There's another scientist called Viktor Zhdanov who was involved in the smallpox eradication campaign, and he persuaded the World Health Organization to actually start working on it, when they were really skeptical before.

Jacob Trefethen:
Good man. Victor-y.

Saloni Dattani:
Boom. He is the mascot of Works in Progress magazine. He's the little guy.

Jacob Trefethen:
That guy with the mustache?

Saloni Dattani:
Yes.

Jacob Trefethen:
Okay. Good on him.

Saloni Dattani:
Pretty cool. Anyway, you have a smallpox vaccine, and for 90 years, you don't have any other vaccines. This is because of all the challenges that we mentioned. The fact that cross-protection isn't that common, that even if it is, it's hard to find a mild version that's easily visible. Then the fact that you don't know about germ theory, you don't necessarily even know about microbes at all. You don't know how immunity works. You don't have a systematic way of producing new vaccines. How do you move forward from here?

Jacob Trefethen:
Well, let me cheat by trying to work backwards from, I happen to know what the next vaccine was, which was the rabies vaccine. Now, will that give me a hint?

Saloni Dattani:
Well, that was the next human vaccine, but there were two animal vaccines in between.

Jacob Trefethen:
Oh, interesting. Okay. I think I'm stuck. You're going to have to help me.

Saloni Dattani:
I think at this point, you probably need to figure out germ theory, and...

Jacob Trefethen:
Right, that would help a lot. Yeah.

Saloni Dattani:
You probably want to be able to have a sense that microbes are spreading these diseases, and we can study these microbes in the lab or in controlled conditions, and we can do something to them that will turn them into a vaccine from being a dangerous pathogen.

How would you work out germ theory? This is so crazy to me to think about, because it's just something that we take for granted today. How do you figure it out from the beginning?

Jacob Trefethen:
Well, let's take it step by step. You can do a bunch- there's the John Snow story, which we may have covered in a previous episode, where you're basically doing epidemiology to try and rule in or rule out competing theories that make sense of the evidence in front of you. I'm wondering though- bacteria are big enough that you should be able to see them if you can somehow make a bit of progress in microscopy. Viruses are like, "good luck." That's not going to- rabies is caused by a virus. I'm thinking they must not be able to see the rabies virus yet.

Saloni Dattani:
No.

Jacob Trefethen:
I guess we don't even need microscopy yet. I take it back. I take it back. What do we need instead?

Saloni Dattani:
I think what we need instead is methods to culture bacteria or microbes in the lab. Pasteur is obviously famous for pasteurization and for fermentation and his experiments in that. But I think that the way that he got into this, he started by trying to debunk spontaneous generation, which was the alternative to germ theory at the time.

Jacob Trefethen:
Maggots.

Saloni Dattani:
Maggots, correct. The popular alternative was essentially that life was formed spontaneously, just came out of nowhere. That rotting meat had maggots that appeared that kind of came out of thin air, just came from, again, bad air or bad smells, bad environment, soil, something like that. There wasn't really a concept of where the maggots are coming from apart from that.

There had been a few attempts to try to disprove this. One of the first ones I read was actually in the 17th century. So 1668, there's an Italian doctor, biologist and poet called Francesco Redi.

Jacob Trefethen:
Was everyone a poet back then?

Saloni Dattani:
I mean, presumably you would have to be somewhat rich to publish your poetry.

Jacob Trefethen:
Was it a bit like how everyone who is a scientist called themselves a philosopher? Was everyone who wrote anything, did they call themselves a poet?

Saloni Dattani:
No, he actually wrote and published poetry; books that were just pure poetry.

Jacob Trefethen:
Okay, okay.

Saloni Dattani:
But I did find that interesting. He did some experiments where he had four wide-mouthed flasks, and he put into them- into each of the four flasks: one of them had a snake. One of them had a river fish. One of them had four little eels. And the fourth one had a cut of meat from a young calf that had been feeding on its mother's milk.

Jacob Trefethen:
Two of them have water in, presumably? Or are you telling me that everything's dead?

Saloni Dattani:
Oh, no, they are dead. They are dead. They are dead.

Jacob Trefethen:
It sounds like a stinky room. I'll just give that spoiler. I'm a fan of the miasma theory.

Saloni Dattani:
Also, I love how this sounds like witchcraft and you're just like, "Oh yeah, you need a tooth from a snake." He has this set of four flasks with the snake, the river fish, the four little eels, and the cut of meat from a young calf. Then he has a duplicate of each of those flasks. But the second one is actually sealed. The first one's open and the second one's sealed, so he has a controlled experiment, right? He observes that only in the open jars do maggots start to appear. The second thing he notices is that in the sealed flasks, there are droppings of flies on them. The flies are probably trying to get into the flasks.

Jacob Trefethen:
Can flies smell through glass or did he sort of somehow? How do flies get attracted to carcasses? I don't even know. Anyway.

Saloni Dattani:
I don't know. I am trying to get into the mindset of a fly and I'm struggling.

Jacob Trefethen:
Okay. But I mean, this is a spoiler for our audience, but you'll never guess what.

Saloni Dattani:
What?

Jacob Trefethen:
Maggots do come from flies.

Saloni Dattani:
Yes! So, the last thing that he observes is that he waits and he watches the maggots and eventually they turn into flies. He has this- he likes to interpret all of his experiments through biblical passages. So he has a famous adage that is, "omne vivum ex vivo" which is "All life comes from life." That's how he explains it.

Jacob Trefethen:
Which, of course, can't be true because- but anyway, it was a nice thought. I mean, that's so interesting as well to think that if someone had just paid attention to maggots for a bit longer, they didn't actually need to do a controlled experiment. They just had to see them turn into flies. It's like, they're coming from nowhere. Then it's like, oh, no, no, they're actually turning into flies.

Saloni Dattani:
Well, I guess that's true. But where would the initial maggots come from?

Jacob Trefethen:
No, you're right.

Saloni Dattani:
It's the chicken and the egg-

Jacob Trefethen:
It's the chicken. You're right, you're right, you're right. You need to see the droppings here.

Saloni Dattani:
Yeah. But sadly, some people still weren't really convinced by his experiments. I guess they just were like, "Yeah, okay, but those are maggots. What about everything else?" It took another... took another two hundred years for Pasteur to finally disprove spontaneous generation.

He sort of did a similar experiment where he had glass flasks with long, curvy necks that kind of make them look like a swan's neck. He has living material, broth, I think, inside the flasks. All of the ones with that kind of neck stay sterile indefinitely, unless the neck is broken. Just because of the shape of this swanny neck, it's hard for microbes to actually get in and then go up. It's like trapping the dust of microbes.

Jacob Trefethen:
But wait, what does that show?

Saloni Dattani:
I found that bizarre, though. What does that show? I think I preferred the other example.

Jacob Trefethen:
That one is, let's just say, on the more boring end, relative to eels and snakes. I love it in the last one. It's like, you didn't need all of those snakes. You're like, "But I have a spare eel. I have a spare snake. Look at this calf. Let me duplicate each of them." Everyone's like, "Wow, that seems really necessary for the experiment. This poet's really onto something." This whole time, you could have just had one swan neck.

Saloni Dattani:
He's really over-egging it. All you needed was a broth in a flask. But I guess the point was this one flask, it is still open on the side, so air can get through. That, I think, would have disproved the idea that it was miasma. But dust and microbes wouldn't be able to get through that whole concoction.

Jacob Trefethen:
Okay.

Saloni Dattani:
Sorry, that does make it sound better than the other version, I'm sorry.

Jacob Trefethen:
No, no, no. I mean, I think there's also another, like maggots and flies and droppings you can visually see. You have to get a bit cleverer to get at the microbe question. So fair enough to our man.

Saloni Dattani:
True. I think this was essentially a very, I think, elegant experiment to show that spontaneous generation was not happening there. He continued working on fermentation; Pasteur was working in the wine industry, and in the silkworm industry, and trying to develop ways to prevent contamination from developing, like preventing spoilage. The famous thing that he invented is a process that's now called Pasteurization.

He briefly heats the wine to 50 to 60 degrees and that would kill microbes and not ruin the product and eliminate the spoilage. Supposedly, these studies were so important that he essentially rescued the French wine industry at the time through developing Pasteurization. The French wine wasn't getting spoiled.

Jacob Trefethen:
Well, I thank him, I've actually drank French wine myself, so thank you, Pasteur.

Saloni Dattani:
So have I!

Jacob Trefethen:
It's amazing to think, though, that with spontaneous generation, I assume that people were thinking about life, and life as the important unit. "Oh, I can see my bread molding and my wine going off. Is there some life that's causing that?" Then, in fact, viruses aren't alive. They probably didn't know much about the distinction between these bacteria that were causing their wine to spoil and the viruses that actually weren't alive, but were using the machinery of some things that were alive. The next vaccines were not against bacteria. But those nuances are so... they're not nuances, they're deeply important. And yet, you don't have to know it all at once. You can sort of hack your way there.

Saloni Dattani:
Right. You actually, it really takes until after the first vaccines are made, and it takes until the 1930s for people to confirm what viruses actually are.

Jacob Trefethen:
1930s, wow.

Saloni Dattani:
Until then, there's just like, "What is this? It's something that is infectious. We can't see it. We can't culture it in the lab." Because viruses, as you said, are not alive. They need cells to grow; they're obligate parasites. It was really hard to culture them. Also, people had developed bacterial filters, and that would filter out all the bacteria, but the viruses would still get through. They were just like, "What is this? Maybe it's a fluid." There was a popular theory that viruses were actually a fluid. It was only in the 1930s that that was resolved through microscopy and crystallography.

Jacob Trefethen:
Wow.

Saloni Dattani:
But we're getting ahead of ourselves.

Jacob Trefethen:
We're getting ahead of ourselves. Back to the 19th century.

Saloni Dattani:
Back to the 19th century. The first vaccines after Jenner were for chicken cholera and animal anthrax. Pasteur went into the animal industry and he's, okay, he's protected the French wine industry. He's protected the silkworms from getting disease. Now, can he protect the chickens? Do you think he's going to succeed?

Jacob Trefethen:
If you've already achieved the most important feat of humankind, which is protecting the French wine industry, I think something as easy as chickens, I think he's going to be all right. He's going to get there.

Saloni Dattani:
He's going to get there. But it turns out he didn't do it. This was so weird to me because I was like, oh, Louis Pasteur, he develops the chicken cholera vaccine, he developed the animal anthrax vaccine, and then he developed the rabies vaccine. But, and this is going to be controversial, and I hope there aren't French listeners who hate me for saying this, it turns out that a lot of the big, the key, steps here were actually by his assistant, Émile Roux, well, who I guess is also French, so.

So he's trying to protect chickens. He's trying to develop a chicken cholera vaccine and doing lots of experiments in his lab. Then he actually goes away traveling to a different part of the country. Meanwhile, without his knowledge, his assistant, Émile Roux, is doing loads of experiments. He tries out different processes and he finds out that some of his cultures are going sour if he just leaves them out for a while. And once he then uses those cultures and injects chickens with them, some of those chickens are actually surviving chicken cholera, and all of the other ones are dying. Chicken cholera was really fatal to chickens, but the vaccine seemed to protect some of them. He was kind of surprised by this and he wrote down these observations.

When Pasteur returned from his travels, they continued doing these experiments and trying to figure out how to replicate that. What are the environmental conditions that are actually causing this broth to go sour? How are we- Is there a reproducible way to make chickens immune? They eventually figured out that it was the prolonged oxygen exposure and the acidity that was weakening the bacteria and protecting the chickens.

Jacob Trefethen:
So, okay, let me take it more slowly. Firstly, you're saying you don't want French people to be mad at you, but you're saying French culture is going sour. Okay, interesting. I'm going to put that out there. Secondly, you're saying that, Émile Roux, was he younger, which I think of him as a PhD student kind of vibe?

Saloni Dattani:
Yeah. You should think of him as a younger- so Pasteur was a chemist. Émile Roux was a doctor. Actually, a lot of the key experiments are done by Émile Roux because he knows how to work with animals and humans. So he is doing a lot of the actual experimentation. He's inoculating people.

Just to summarize this chicken cholera vaccine, we're kind of exposing the broth that contains the chicken cholera to oxygen for a long time and acidity for a long time. That is a method that's called attenuation, so you're weakening the pathogen and it sort of evolves into a different strain that is unable to cause severe disease in chickens through these different environmental conditions. Pasteur is really now talking about his theory of how this is working, that it's weakening the microbe, it's sort of changing it, and this is the way that you should be developing new vaccines.

He then turns to anthrax. Animal anthrax was, again, really deadly for different types of farm animals. He's like, let me try to develop another vaccine with the same method that's going to protect them. What is so funny about this to me is that he does a live demonstration to test whether this vaccine works. I think this is odd to us now because people don't do that anymore. But it feels a bit like...

Jacob Trefethen:
"Gather round!"

Saloni Dattani:
Yes.

Jacob Trefethen:
Sorry, wrong accent. [over the top French accent] "Come, gather round!"

Saloni Dattani:
Very good. So 1881. Pasteur is at Pouilly-le-Fort in France, and he's at a farm.

Jacob Trefethen:
That was the name Fort of Chickens, I think.

Saloni Dattani:
Pouilly-le-Fort.

Jacob Trefethen:
"Hey, Pasteur, where are you headed this weekend?" "Ah, Pouilly-le-Fort."

Saloni Dattani:
So he's going to publicly demonstrate that his animal anthrax vaccine, which he's also developed through attenuation, is going to protect the animals. He gets 58 sheep and 10 bovines: eight cows, one ox, one bull. He brings them together for this experiment. Half of these animals receive the attenuated vaccine that he's made of anthrax. Two weeks later, they get revaccinated with a more virulent, less weakened version of the microbe. And then, another two weeks later, all of them are injected with a highly virulent, fresh culture of anthrax. Over the next few days, we're going to see what happens to all the animals. He invites people from around the country to come and see the results of his live experiment. What do you think is going to happen?

Jacob Trefethen:
Oh, I think that some of them are going to make it and some of them are not. That's my guess.

Saloni Dattani:
You are, well, it was actually quite successful. It turns out that in the vaccinated group, all of the vaccinated sheep, the goats and the vaccinated cows were healthy. In the unvaccinated group, most of them died- had already died by the date of the observation when everyone came to visit them. Then two more sheep died while people were viewing the results of the experiments, and the last unvaccinated sheep died later that day. Basically all of them died.

Jacob Trefethen:
That is lethal anthrax.

Saloni Dattani:
Yeah, it's very lethal. The unvaccinated cows didn't die, but they did have a lot of swelling. So he's like, "successful experiment! I have proved the efficacy of my new vaccine." And that's true. I remember when I was reading this, I was like, "Wow, why don't people do live demonstrations anymore? That would be kind of cool." You could show live how the method works. You could demonstrate that something replicates.

Jacob Trefethen:
You could do it more easily now because you can livestream.

Saloni Dattani:
Very true. I was kind of disappointed and was a little bit surprised to actually read a bit more about this experiment and what happened behind the scenes and before the experiment proceeded.

What is really odd about this is that Pasteur's lab notebooks and also just generally some of his methods, he kept secret for most of his life. Only after he died were they published by his former assistants. By looking through those notebooks, historians have found out that he didn't attenuate the vaccine. He actually used a different preparation. He used a different preparation that was made by his assistants, Émile Roux and Charles Chamberland, and they actually chemically inactivated the bacterium with potassium bichromate instead.

I was like, "But why would you hide that?" It still works, right? Turns out the reason was that he had a rivalry with this other scientist called Henri Toussaint. His rival had already published similar results using carbolic acid. Basically, Pasteur was trying to show that his vaccine was better and that attenuation was the key principle to developing vaccines. So he told them not to tell anyone about how the actual preparation was made until after he had died.

Jacob Trefethen:
That is so sketchy. Also, what did he think was going to happen to his reputation after he died, if all these secrets are coming out? And then fast forward to 2025, two people are roasting him on a podcast.

Saloni Dattani:
Well I mean, I didn't know the story until I looked into it in the last few months, so I think most people didn't actually know that.

Jacob Trefethen:
You run the parallel in the modern system and it wouldn't work. The pros and cons of patents are numerous. But one of the pros is that if you file for a patent, it does get made public. Your competitors do know what is in your concoction. Even if you don't file for a patent, you have to let the FDA know if you're in the US, or MHRA if you're in the UK. They probably won't leak it though, they'll treat it as a trade secret. But now that we have so many more scientists, if you actually sell a product or you put a product on the market, your competitor is going to be able to just buy a vial of it and then see, "hold on, what's in it?"

Saloni Dattani:
Yup. I was also thinking at the time, wait, how were other people making the animal anthrax vaccine that- if they followed the method that he claimed he was using, they wouldn't succeed? But I think his institute, which was a very big research institute at the time, was producing this for most of France. So they just had the method-

Jacob Trefethen:
They were doing it secretly, and everyone was injecting their animals.

Saloni Dattani:
Animals, yeah. It was working. It was a different vaccine.

Jacob Trefethen:
That's ridiculous.

Saloni Dattani:
Which I think is crazy. I guess I thought maybe live demonstrations are not good after all, because maybe the stakes are just so high that you want to avoid humiliation and you're going to do whatever it takes to do that.

Jacob Trefethen:
Yeah. Whereas a good experiment, you want to be learning, which means there has to be a chance of success and failure. Otherwise, you're not learning anything.

Saloni Dattani:
Yes, yes! There has to be a chance of failure. But anyway, I mean, it was just such a bizarre. I was like, "Wait but... why don't you just tell people the truth?" Anyway.

Jacob Trefethen:
Never meet your heroes. That's why I really regret meeting Louis Pasteur.

Saloni Dattani:
Anyway, he did do amazing things with fermentation and pasteurization. Now he turns his eyes to rabies, which is terrifying because almost anyone who develops any kind of neurological symptoms from rabies then dies from it, usually within a few weeks. Can we develop a vaccine for that? That was probably- and this was a human disease, so unlike the animal experiments, now you're doing something that's potentially risky and exposing humans to it.

So again, as you mentioned, the rabies is caused by a virus too small to be seen under the microscope. But Pasteur and Roux and other people had reliably found that if you took brain tissue from an animal that had rabies, you could use it to cause rabies in another animal. Something in that brain tissue is infectious and is causing rabies. Don't really know which microorganism it is, but maybe we can develop a vaccine from that.

Although Pasteur was very secretive, I think one of the good things about his approach to science was that it was very empirical. It was hundreds of experiments that he would actually write down in a lot of detail in his lab notebooks. Many of them were failures and he was trying to learn from what worked. In this case, again, it took hundreds of experiments to develop a rabies vaccine.

The process was this. You would extract brain tissue from a rabid dog and then inject it into the brains of rabbits by drilling a small hole into their skulls and injecting it. Then you do this from rabbit to rabbit. You take the brain tissue out and put it into another rabbit, after drilling a hole in their skull, again and again.

I think eventually they did this through a series of 90 rabbits in a row. They then take the brain tissue and put that into a flask and then close the flask and sort of let it dry to weaken the pathogen. Again, this took a lot of experiments to figure out. What was really difficult was that if you did this in other animals, not rabbits, then sometimes it would actually make rabies more severe. So you really have to be careful in doing this method and you have to be writing up what the experiment showed, what your failures were, how does this actually work?

Jacob Trefethen:
Instead of live attenuated, you might get live boosted.

Saloni Dattani:
Exactly, which is terrifying. Then you inject that material into dogs and sort of gradually expose them to higher and higher doses from the rabbits. As you continue doing this, exposing the dogs to higher, more virulent strains, you are helping them build up protection. And that actually seems to work. Louis Pasteur felt comfortable enough to move to treat people with this procedure.

Again, you're hoping that it's not worse in humans because humans are not dogs and you haven't tested it before in humans. That's quite scary. You are also doing this procedure where it's not just once and done. You have to give them the lowest dose and then higher and higher. You gradually help them build up protection after they have already been infected.

Jacob Trefethen:
They've been infected and you're very quickly doing this process.

Saloni Dattani:
Yeah. So he actually treated people bitten by rabid animals, who I guess wouldn't have had really any other alternative. They were quite desperate for having some treatment and Pasteur says that he might have developed some method. He treats different people. In 1885, he and Émile Roux treated two young boys that were bitten by rabid dogs. They seemed to be fine after it. Almost everyone else would have died and they survived. This was the first sign that the procedure actually worked. That was a big breakthrough and Pasteur was very, very happy about it.

Jacob Trefethen:
I suppose that Frankenstein was written much earlier in the 19th century than this, but you can sort of get why people had a view of scientists that was kind of like, what the hell are they up to? Yeah, "I just want to drill a hole in this rabbit's brain, so I can inject its brain into a dog, and then inject the dog's brain into a different dog." Like, what the hell are you doing?

Saloni Dattani:
Sometimes you're playing with eels and you're growing smallpox on cows.

Jacob Trefethen:
It's like, why can't you get a normal job like chimney sweep or something?

Saloni Dattani:
This reminds me of how surgeons, surgery used to be seen as this very low status and very just physical procedure that it was literally just someone who's ready to chop off someone's leg, basically, because there weren't really any; there are very few surgeries that were worth the risks at that point, before Joseph Lister developed antisepsis. So you would only do it in the highest risk situations. You would maybe have a kidney stone removed. You would maybe have your leg chopped off if it was at risk of gangrene or something like that. There were surgeons who had trained so much in doing this that they could do a whole procedure of cutting off someone's leg within half a minute.

Jacob Trefethen:
What? Oh, God. You want to do it quickly, I suppose, otherwise it'll go.

Saloni Dattani:
Exactly, because it's so painful as well. Because until 1846, no one had developed anesthetics either.

Jacob Trefethen:
You know, you could tell me that these doctors were drilling holes in people's brains and administering vaccines there and at this point, I might believe you.

Saloni Dattani:
You know I read this very short, probably apocryphal bit about how there was this famous surgeon in the mid-19th century who had perfected this technique so much that he was famous for doing his surgeries within half a minute. One time, he accidentally chopped off someone's testicles as well.

Jacob Trefethen:
No, come on, Saloni. Come on. God, going back within time is...

Saloni Dattani:
You don't have modern vaccines. The vaccines you do have are developed by drilling holes into rabbit skulls.

Jacob Trefethen:
I didn't know that story of the rabbits and the dogs. But I do think of the rabies vaccine as helping to confirm the germ theory of disease. So, I guess, what are they learning there that's generalizable to the theory?

Saloni Dattani:
I actually, I'm not sure that it is- well, it is helpful, it's the first human vaccine after Jenner's vaccine, so that is definitely a big moment, but because you couldn't- they couldn't figure out what the microorganism was, it wasn't that helpful for germ theory. Pasteur was kind of repeatedly asked by other scientists, "What's causing this disease?" He was like, "We haven't found it yet. We're focused on the experiments. We've made the vaccine. It works." He didn't know, and he couldn't have known.

Jacob Trefethen:
It's amazing you'd have the persistence to keep doing so many weird steps in order involving so many animals' brains when you just don't have an understanding of what you're doing. It's amazing.

Saloni Dattani:
I guess because he had worked on fermentation. He was also just much more of an empiricist than a theorist. He was like, I've developed this method. It's going to work. I'm just going to do this procedure. Somehow, for some reason, it's going to work and I don't know why, but it will, eventually. And he just does hundreds of experiments to try to figure out how.

But no one figures out what a virus is, or actually looks like, until the 1930s. There's no way that he could have actually found that out. But I think what really helps was germ theory; was actually Robert Koch and him developing Koch's postulates, which you might have heard of, and also just identifying different microbes that cause different diseases. He had four postulates, and if you fulfilled these four postulates, you would establish causation between a microbe and a disease. And not so similarly, but I was surprised to learn that Koch didn't actually compile the postulates into four and he did not say that you needed to fulfill all four to establish causation. It was actually his student, Friedrich Löffler, who puts them together into a textbook.

Jacob Trefethen:
This is happening a lot. Students getting their work stolen constantly.

Saloni Dattani:
No but in this case, Robert Koch actually did mention in different places each of these four postulates. He just didn't say that you needed to fulfill each one. So here are the four postulates. Number one, the microbe or a particular microbe has to be found in every case of the disease. Second, it has to be isolated and grown in pure culture. Third, it must cause the same disease when introduced into another healthy host. Fourth, it must then be recovered from that host.

What do you think? Is this going to help? Is it going to cause problems?

Jacob Trefethen:
I think it's going to help. You're going to get some false negatives, probably, would be my guess.

Saloni Dattani:
Yes. I think it definitely did help and it sort of increased the level of scientific rigor and what the threshold was for establishing whether a microbe was a cause for disease. I think partly as a result of him putting together these postulates and people having a systematic way of testing, is this microbe the one that's causing the disease?

I think it just means it's probably one of the reasons why most of the microorganisms that people traced back at that time still hold up today. I think that is something that's quite impressive. There were dozens that people discovered during this time period of the late 1800s. Tuberculosis, cholera, typhoid, diphtheria, tetanus, meningitis, pneumonia. People discovered some of the microorganisms that caused all those.

But it has a lot of problems as well, because if you think about each of these four postulates, the first one: the microbe has to be found in every case of the disease. That's really strict.

One thing that's difficult about this is viruses are kind of ruled out at this point, because you can't see them. So it's very difficult to identify when they're the cause of disease. Second, there are some diseases that have multiple causes like meningitis or pneumonia; they have different bacterial and sometimes different viral causes as well. So maybe you're hoping that people can classify them more granularly and say, oh, well, 'the bacteria does cause pneumonia, but only this version of pneumonia' or something. But to me, it feels very strict as a definition.

Then there's the other one, the second one, which is the microbe has to be isolated in pure culture. Sometimes that's really hard, right? It's really hard to grow some microbes in culture or in other animals.

Jacob Trefethen:
Syphilis is caused by a bacteria, Treponema pallidum, not by a virus. But only in 2016, '17 or '18, around then, did people first have a protocol for in vitro culture. You used to have to culture it in rabbits.

Saloni Dattani:
Wow, that's so much later.

Jacob Trefethen:
So much later, yeah.

Saloni Dattani:
These kinds of difficulties actually tripped up Robert Koch as well. He often struggled to satisfy the postulates that he had developed.

Jacob Trefethen:
You can be your own worst enemy sometimes.

Saloni Dattani:
Yeah, sometimes you regret the things you write. But maybe rules are just meant to be broken. So he tried to figure out what the cause of cholera was, and he did very quickly actually isolate the bacterium, which is Vibrio cholerae, from patients who were dying in Egypt and India from the disease.

But he couldn't figure out how to reproduce that in other animals. He couldn't reproduce it in culture. He couldn't grow it in culture. He tried repeatedly to inject mice and other animals with it. He took fifty mice from Berlin to Egypt to test whether they could get infected, and none of them developed cholera. Then he just asked people; he was like, "Are there any animals that get infected by cholera?" And the answer was no. So he was really struggling.

He writes in this report in 1884, "No one ever observes animals with cholera. Therefore, I believe that all the animals available for experimentation and those that often come into contact with people are totally immune. True cholera processes cannot be artificially created in them. Therefore, we must dispense with this part of the proof." So he acknowledges that. Sometimes it's just really difficult, and you don't necessarily need to have all of these four postulates fulfilled, but they are a really high bar that I think makes you, it makes me very confident in some of the pathogens that actually fulfill all of them.

Jacob Trefethen:
Right. That makes sense. Yeah.

Saloni Dattani:
The thing is, though, when he said this, the fact that, oh, well, we must just dispense with this part of the proof, other people were not convinced by that. He had another rival. He was also rivals with Louis Pasteur, but he had another rival, Max Joseph von Pettenkofer, who was a chemist and a hygienist. He was like, "No, cholera is spread by dirty soil and dirty air. It's miasma, it's hygienic conditions, it's not germs." He wasn't convinced by Koch's rules that he broke himself. He was like, well, we can see that cholera is much more common in the places with worse hygiene and sanitation. That's even true today. But he basically thinks that it was soil and air that just spread disease and it just came out of nowhere. It wasn't spread by microorganisms that you could see.

Jacob Trefethen:
It's funny to think today we have all of these separate subfields of, on the one hand, epidemiology, on the other hand, microbiology, on yet another hand, vaccine development. Back in the day, everyone was kind of doing everything all at once. They were trying to make progress all at once, and there were about three people doing it.

Saloni Dattani:
You'll love this next step of the story then. Because the way that he then proves that cholera is caused by this microbe is by doing epidemiological analysis. He can't replicate this infection in animals. Instead, he tries to find more evidence. He finds, surprisingly, that there are two adjacent cities, Altona and Hamburg- for some reason, on the Hamburg side, there's a lot of cholera and people are always facing outbreaks. On the Altona side, people are just free of the disease. He was like, what is going on? And this is even true just at the boundaries.

He looks and he compares different aspects of those two streets and those areas. He's like, well, the soil is the same. The sewers are the same on both sides of this boundary, but the difference is their water supply. He then studies the water supply and finds the same bacterium there; he finds cholera that's present in the Hamburg supply, but not the Altona water supply. And this resolved the debate. Mic drop.

Jacob Trefethen:
Mic drop!

Saloni Dattani:
The other thing that I didn't know until reading about this was that there was a political divide in this debate as well. The germ theorists versus the sanitationists. In Germany at the time, the idea was the sanitationists want to improve living standards, they want to improve, they want to reduce poverty. The germ theorists are like, you don't need to tackle poverty; you can just eliminate diseases by vaccinating against them. I don't know. I just found that very different and interesting. But of course, they're not actually distinct. You can reduce the chances of microbial growth and infection by improving sanitation and hygiene. We know that now.

Jacob Trefethen:
With cholera, you can do both. People do do both right now.

Saloni Dattani:
People do do both. The sanitationists actually had a lot of victories in the 19th century because they introduced various sanitary reforms and improvements to water supply and air and getting rid of mosquitoes and keeping people away from sewers and things like that. That actually reduced a lot of different infectious diseases. I think in a way, maybe they were kind of right, but in another way they were wrong, because they didn't understand exactly how the diseases were spreading and the fact that vaccines would work.

Jacob Trefethen:
If the sanitationists had been in power all the way through, we would not have got the smallpox vaccine and we would not have got smallpox down because that, you gotta use the vaccine.

Saloni Dattani:
It would be really hard to eradicate some diseases if you were just using sanitation and hygiene as your tools. Okay, so we've talked about how the first vaccine was made, Jenner's vaccine, through cowpox. We've talked about then how the next vaccines were made through attenuation, getting the microbe to grow in a different environment and weakening it, so that it causes a milder disease when it's then injected into humans or into animals. Or there's inactivation, where you kind of kill or inactivate the pathogen in different ways, with chemicals or oxygen or something like that. This is quite a helpful technique, but I think the real breakthrough comes with better methods of culturing bacteria in the lab. So now we need to talk about culture.

What is kind of interesting about this is that really until the late 19th century, there aren't great ways to grow bacteria in the lab. I don't know if you know this, but in the past, people used to grow bacteria on slices of boiled potato.

Jacob Trefethen:
Eugh.

Saloni Dattani:
You could also grow them in broths of different- fluids, that's kind of gross.

Jacob Trefethen:
The boiled potato though, I mean, that's perfectly fine. Not gross at all.

Saloni Dattani:
Well, not if you're growing... anthrax bacteria on it. So Robert Koch was working on anthrax as well and trying to identify the bacterium. He was working with anthrax bacilli on slices of boiled potato. It made me think, what if someone accidentally ate them?

Jacob Trefethen:
Yeah, that's dangerous, especially if they're lying around looking tasty. You might think it's sort of like a blue cheese spread or something.

Saloni Dattani:
Mm... true. You have these liquid media, you have the broth and you have the potato slices. They're not that great. They don't work with too many bacteria and they're not very easy to standardize. There's this need to get some better culture method. Maybe you can find some way to grow bacteria on a solid substrate.

An ingenious idea was to use the existing liquid broths and then just solidify them. That was what Robert Koch did. He just solidified the broths with gelatin, but it didn't work because it melted in the summer. Gelatin just doesn't stay stable at higher temperatures, so in the summers, it would just melt and that would ruin a lot of experiments. The solution to this was to, instead of using gelatin, to use agar. Agar is a gelatinous material that comes from seaweed. This idea came from the wife of the assistant of Robert Koch. Her name was Fanny Hesse.

Koch had just developed this tool where it's like a plate, and then there's a solid broth, solidified broth, and it's covered with a bell jar. That was an interesting concept. Then he had an assistant come along, and the assistant's name was Julius Petri.

Jacob Trefethen:
I heard he was quite dishy.

Saloni Dattani:
He thought of a better method, which is also very simple, but it was just remove the bell jar and just add another dish that's slightly larger. You'd have a flat, a lidded dish. Why not just use two dishes?

Jacob Trefethen:
Right. Sounds quite simple.

Saloni Dattani:
It is quite simple, but it's so useful. You could keep the cultures sterile from other microbes growing in them because that second lidded dish would make it really hard for microbes to get inside. But you could still observe everything happening on the plates.

So this combination of agar, Petri dishes, other bacterial culture methods made it possible to grow colonies of bacteria, to experiment with them, to visually identify the microbes, and then eventually to turn them into vaccines.

Jacob Trefethen:
To visually identify the microbes.

Saloni Dattani:
... under the microscope. The bacterial cultures, this method is really useful to grow bacteria because they can just eat the nutrients in the broth and grow. That means that you can develop a lot of bacterial vaccines out of that. You can grow the bacteria in the lab, you can study them, you can evolve, you can attenuate them, you can inactivate them. It doesn't work with viruses, because viruses need cells to grow in, and we don't yet know how to grow cells in a lab.

Jacob Trefethen:
I have a question, which is, nowadays, when you're culturing bacteria for the sake of making vaccines, I mean, if you're making a vaccine, some of those bacteria are probably kind of dangerous. You have special lab conditions to make sure that you don't yourself get infected and you don't pass on an infection. In the 1880s, 1890s, 1900s, what were conditions like? Were people good at avoiding infections?

Saloni Dattani:
Well, quite scary because they hadn't developed antibiotics back then.

Jacob Trefethen:
Oh my gosh. Yeah, of course.

Saloni Dattani:
They did have some antiseptic techniques, but they hadn't been introduced into culture methods yet. They also were still mouth pipetting at this point, I'm pretty sure.

Jacob Trefethen:
They were mouth pipetting while doing bacterial culture vaccines.

Saloni Dattani:
Very scary stuff.

Jacob Trefethen:
Yeah.

Saloni Dattani:
Maybe you would just need a scoop, you could just get a spoon or something and just streak a bacterial colony onto the Petri dish. You could probably get infected by stuff. Some people would deliberately infect themselves as well because they wanted to prove that something caused a disease. So when Robert Koch was trying to demonstrate the bacterium the caused cholera, he couldn't find any animals that it could infect. Not him, but other scientists who really believed him were like, 'well, let me just try to ingest the cholera and see if it causes disease in me.' I'm not really sure whether that worked, but it wasn't very convincing.

Jacob Trefethen:
Yes, it used to be a bit more direct back then.

Saloni Dattani:
The other thing that people were learning at this point was that organisms were composed of cells. People didn't know that before. I found that also so strange. They were just like, well, we're just made of material, I guess, stuff. We just appear out of nowhere.

I think at some point microscopes got good enough that you could actually see individual cells and people started to notice that, oh, there are a lot of things that have similar looking blobby cells, are composed of them. One by one people had to demonstrate this was true for many different organisms. Eventually they're like, maybe cells are the units that all living organisms have. But that took a long time. They didn't know that that was kind of- you would just think, 'well, it's just a person. It's just a person that gets bigger and bigger.' We're not made of cells. We're just...

Jacob Trefethen:
That's how I-

Saloni Dattani:
We're just like an inflatable.

Jacob Trefethen:
That's my, yeah, the miasma theory of human. You're just bad air that keeps getting bigger.

Saloni Dattani:
I feel like I'm imagining a little baby or a fetus and then it's just getting inflated and inflated and turned into an adult.

Jacob Trefethen:
Well, how would you disprove it? Could be true.

Saloni Dattani:
Could be true. So microscopes then become really important and they were not very good before the 1830s because there are a bunch of lens distortions. Eventually Joseph Lister's father, who was a wine merchant, was also a lens maker in his free time.

Jacob Trefethen:
Everyone was everything.

Saloni Dattani:
He was just like, 'oh, I like microscopy, I like looking at stuff under the microscope.' He developed better lenses that corrected some of these distortions. Because of all of this development, you could actually see bacteria quite clearly. It wasn't just blurry blobs under a microscope. The most famous example of this is Robert Koch identifying the bacterium that causes tuberculosis. I don't know if you know the story behind that, since you're a big TB fan... or a hater.

Jacob Trefethen:
Not really, tell me.

Saloni Dattani:
I think maybe we could just describe the process of how microscopy works. You're not just putting a culture under a microscope because bacteria are not colored necessarily. It's hard to see them and they can be quite translucent, so you need to stain them with some dyes. You have staining techniques, and then you have to get the culture or whatever material really thin so that you only have one layer and it's not just blobs of different bacteria or microbes. There are a bunch of innovations in making better fixing methods and better staining methods and better slicers and things like that.

The difficulty with tuberculosis is that bacteria usually repel most water-based dyes. All the standard dyes that people were using at the time didn't really work, and it was really hard to stain, and people couldn't really see what was causing the disease. The key innovation was that Robert Koch took lung tissue from an autopsy of someone who had tuberculosis and he had the standard dyes and he then added ammonia. The ammonia somehow meant that the dyes were now working and the dyes were staining the bacteria's cell walls. The reason for that was that bacteria has acidic cell walls and the ammonia makes it more alkaline. That makes it easier for the dyes to attach to the bacteria. This meant that he could finally see the tuberculosis bacteria, Mycobacterium tuberculosis, in 1882.

The other thing that I found quite funny was that he was not very- at the time people were doing microscopy and then they were drawing the results that they were seeing, but he was very bad at drawing. Well, he wasn't very bad, but it's not looking good. He was trying to find a better way to visualize this and he really wanted to reproduce his work. He thought maybe we can attach a camera to a microscope. He basically worked with microscopy developers to make a photomicroscope with a camera attached to it. He then got lots of pictures of his discoveries and they became really famous. It basically showed visually diseases are being caused by specific microbes that are moving around, changing shape, and you could actually identify their causes. It was a huge revelation.

Jacob Trefethen:
That's epic.

Saloni Dattani:
The other thing that microscopy would be really helpful for is that you could then see if your preparation was contaminated. You could see if there were other microbes infiltrating the culture that you had. You could develop safer vaccines. You could do experiments more reproducibly and things like that, because you're actually working with the correct microbes in the lab each time.

Jacob Trefethen:
We've gone from not knowing what caused these diseases we were trying to make vaccines for, to knowing the cause in some sense, but not being able to see it or control it, to we're now growing cultures of that cause, those bacteria, in an agar plate, in a Petri dish. We are dyeing those, so we can see them and we're looking at them under a microscope.

Saloni Dattani:
Yes. Now the challenge is, okay, let's actually use these tools and make many more vaccines. Some people do actually do that. There's a new cholera vaccine and a new bubonic plague vaccine, and then there's a typhoid vaccine in 1896. There are a bunch of bacterial vaccines.

But again, virus vaccines are still really hard because you're growing them in other animals. You need to find a way to keep cells alive for long enough that you can study the viruses that grew in them. I don't know if you know what happens at this point, but the key moment that I've read about is the hanging drop technique.

Jacob Trefethen:
The hanging drop technique, yes. Your opponent is on their back after a blow, and you actually get on the corner of the wrestling ring, and you stand on both of the railings, and then you...

Saloni Dattani:
Jump on them.

Jacob Trefethen:
Yeah.

Saloni Dattani:
But it's much less exciting than that.

Jacob Trefethen:
You're telling me there's a second hanging drop method?

Saloni Dattani:
Yes.

Jacob Trefethen:
Oh, how does that work?

Saloni Dattani:
The second hanging drop method is actually really simple. You have a microscope slide, you take cells from a frog embryo and then you put that into frog plasma, and you put that on the microscope slide, and then you turn the microscope slide upside down.

Jacob Trefethen:
Ooh. How did someone come up with that? Who came up with the hanging drop and what does it let you do?

Saloni Dattani:
Ross Harrison, who was at Yale. I think he was trying to find a way to visualize cells under a microscope. They kept dying if he kept them upright. He just put them upside down so that the drop was bigger and the cells would have much more fluid and they could grow for longer. He could still see it with the microscope by seeing the other side of the microscope slide.

Jacob Trefethen:
Cool.

Saloni Dattani:
He did that with neurons and he saw them growing for weeks and sometimes months, sitting in that little drop, which I think is so cool. Over the 1910s and '20s and '30s, people made many new cell culture techniques. They found different cells that viruses could infect in the lab. That helps develop a lot of different vaccines.

If we think back to the smallpox vaccine, that was growing in calves. The rabies vaccine was growing in the brain tissue of rabbits. The influenza vaccine is growing in embryonated eggs. Polio vaccines were made in monkey kidney cells.

Of course, at this point, people actually develop better techniques for sterilization. One of them is antibiotics. Another is autoclaves. I actually didn't really know how autoclaves worked until recently. I was like, they just somehow sterilize equipment. It turns out it's just a lot of steam.

Instead of the Petri dishes and the microscope slides, people develop other better techniques to have larger surface areas for cells to get nutrients from. One is the roller bottle system, which is just bottles filled with the cell culture and fluid and stuff.

Jacob Trefethen:
Still used today.

Saloni Dattani:
Still used today, and it's just on this little machine, and the machine kind of moves from it, and the bottles keep rolling, and that keeps them all...

Jacob Trefethen:
There's something that is quite gestational, maternal about it. It's very sort of like... whoosh whoosh whoosh... rocking a baby.

Saloni Dattani:
Like a little cot. Yeah. Then there are microcarriers, where it's a big tank filled with little spheres, and on the surface of the spheres, the cells are growing and there's growth medium surrounding them.

We still don't have better microscopes to see viruses until the 1930s. This is so crazy that people are sometimes developing virus vaccines basically through a lot of experimentation, but they still don't actually know what is causing those diseases. Again, they know that... They can't see it. They can't grow it in bacterial cultures. Seems like it's growing in cell cultures. They don't know exactly what's causing it. They can decontaminate things with antibiotics and with bacterial filters, but that's not affecting the viruses. They just don't know what the viruses are.

All of that changes in the 1930s when two scientists, Ernst Ruska and Max Knoll, developed the electron microscope. I also, I just don't know that much about physics. I was like, 'What is it? Why is this more helpful?'

The reason is that with light microscopy, the resolution is kind of limited by the wavelength of light. Light has a relatively high wavelength. That means that if any two objects are closer together than half of that wavelength, then it's really hard to distinguish them. That meant that basically viruses and smaller materials just can't be visualized at all.

The difference with electron microscopes is that electrons have a much shorter wavelength than light. That means that they can distinguish much smaller details. In an electron microscope, you have magnetic coils that are the lenses, and they bend the electron beam and focus it onto the sample. All of that happens in a vacuum so that the electrons aren't just scattering around. The beam passes through or bounces off the specimen, and then that pattern is projected onto a screen or a photograph. It's very similar in the overall principle to light microscopy, but instead of light, you're using electrons, and the machine is also much bigger, I think.

Jacob Trefethen:
Electron microscopes are big enough, they're pretty fun to look at because you're like, oh, wow, this is some heavy duty. 'If something breaks down here, I don't know how I'm going to fix this one.' Whereas if it's just a nice little light microscope, I'm like, I'll just replace the lens or something like that.

Saloni Dattani:
This also is kind of interesting because so far we're talking about a lot of these things just being developed through experimentation, but electron microscopes are made through better theory. People figure out that the way that you get better resolution is through either changing the wavelength of light or if there was something with a smaller wavelength of light. They're like, well, electrons have a smaller wavelength than light. They also have to figure out what electrons even are and how they get bent by magnets and things like that. Only after those things were figured out, people were like, let's try to make better microscopes. So they make electron microscopes. I think the first ones were not very good and they had to kind of improve the lenses, improve the vacuum sealing and things like that. Eventually there's an enormous improvement in the resolution that you can get, like thousands of times higher than you could get with light microscopy. That finally allows you to see viruses.

Jacob Trefethen:
When abouts did that happen?

Saloni Dattani:
1931.

Jacob Trefethen:
1931. We had the smallpox vaccine, which is a virus that was making use of cross-reactivity of a different virus, cowpox. Okay. We had the rabies vaccine, which was also a virus, but making use of these rabbit brain attenuation techniques without knowing necessarily what the virus was. The flurry of vaccines that you talked about, so that was 1880s, 1890s, and there was a bunch of vaccines in the decades afterwards. But those vaccines, the ones I think of, are bacteria.

Saloni Dattani:
Mostly bacteria.

Jacob Trefethen:
Right, okay.

Saloni Dattani:
They're mostly cholera, typhoid, things like that.

Jacob Trefethen:
Got it. Because of all the culturing techniques that you were just talking about. It's not until the 1930s we get an electron microscope. Does that then open up the avenue for viral vaccines? Are we back in business?

Saloni Dattani:
That's what I thought. But actually, no. The key thing for developing better viral vaccines is the cell culture techniques. The microscopes are really helpful in identifying some viruses that cause diseases in the first place. Also, they're helpful for classifying and making sure that the vaccines are not contaminated and things like that. But they're not that helpful for vaccine development for a long time. Part of the reason for that is that electron microscopes would destroy biological tissue. The electrons themselves are very harmful and they just destroy proteins and biological material. The next big one is the polio vaccine.

Jacob Trefethen:
The polio vaccine, yeah. That's 1950s?

Saloni Dattani:
That is 1950s, but the key thing that happens in order to enable that is in the 1940s, which is by John Enders, who later developed the measles vaccine. So John Enders and some of his colleagues are trying to figure out how to grow polio virus in the lab so that they can study them better and so that they can attenuate them or inactivate them. They know that polio affects the brain and the nervous tissue, but they don't know how to grow it outside of those tissues in order to attenuate them or study them better.

It turned out that John Enders' colleagues just happened to be working with chickenpox and they were working with diarrhea and they had different samples of these other viruses. John Enders suggested, why don't you try to inoculate some of those extra tubes that you have with poliovirus and see if it manages to survive? It turned out that it did. Some of those tissues that they were using, which were human foreskin or embryonic tissue, was actually keeping poliovirus alive. You could then figure out that there are different serotypes of poliovirus, and then you can try to attenuate them or inactivate them and turn them into vaccines.

Jacob Trefethen:
Serotype meaning it's the same virus, but you can characterize different strains by how the immune response hits them.

Saloni Dattani:
One of them typically doesn't protect you against the other. So, for each of the polio vaccines, you need to develop them for each of the three serotypes. The vaccines are a combination of all of them.

What was so weird about the John Enders bit was how he actually became a scientist at all. So he was previously a real estate salesman.

Jacob Trefethen:
Okay.

Saloni Dattani:
He studied Celtic and Teutonic languages at Harvard. The reason that he changed and started working in infectious diseases was because he was in a boarding house sharing a room with Harvard medical students and one of those medical students was working in this famous lab and he was just captivated by his work and he thought, well, let me just abandon my PhD in English that he was almost finished with and instead do medicine and bacteriology and immunology. So he did that and he joined his roommate's lab, did a doctorate in that instead, and then finally got an appointment in the faculty, he was 32. But again, after being a real estate salesman. It did make me think about these chance events. I'm like, what if he didn't have that roommate?

Jacob Trefethen:
Yeah, that stuff's scary.

Saloni Dattani:
What if no one figured it out for another 10 or 20 years? That would have been really scary.

But building on his techniques, there were two other scientists whose names are probably quite well-known, Jonas Salk and Albert Sabin. They developed the two polio vaccines that are still used today. Salk's vaccine was a killed version, an inactivated version of the poliovirus, which he grew in monkeys' kidney cells and then inactivated with formalin, which is a chemical. That is a very safe vaccine. It can still give you an immune response and you can still recognize the virus later on.

In contrast, Albert Sabin made a live attenuated virus, and it's an oral vaccine. The previous one was injected. This one is oral as a drop, and that has a weakened strain that replicates harmlessly in the gut and then can also protect other people.

And both of them had a rivalry as well. Apparently, they really disliked each other. I was reading this LA Times article about them, and Jonas Salk says in it, there's this quote from him: "Albert Sabin was out for me from the very beginning. In 1960, he said to me, just like that, that he was out to kill the killed vaccine." I was like, calm down.

Jacob Trefethen:
We think of him as a lifesaver, but really he was a killer.

Saloni Dattani:
Albert Sabin, was also like... they just hated each other. He was talking about Salk's vaccine and he was like, "It was pure kitchen chemistry, Salk didn't discover anything." Come on! They're sort of dunking on each other's vaccines at a time when people need to be, I think, more receptive to the fact that you can protect yourself from this scary disease that could paralyze you, put you into an iron lung.

Jacob Trefethen:
I think that Pfizer and Moderna should have come for each other's throats during COVID. "That's a kitchen table mRNA vaccine. I could have made that in my backyard."

Saloni Dattani:
It reminds me of those viral memes where you see someone does a really complicated maths proof, and they're like, how I did this step: trivial. A toddler. I read one today that was like, the proof for this step in the mathematical formula is: ask a toddler on the street.

Jacob Trefethen:
What are toddlers doing on the street? Come on.

Saloni Dattani:
How are they solving complex math proofs?

Obviously, the polio vaccine is kind of amazing because, in the mid-20th century, there were literally hundreds of thousands of cases of people getting paralyzed by polio per year, right? This just basically eliminated it in so many different countries. Two of the serotypes of polio have actually been eradicated worldwide. There's just one left. We don't anymore have to see lots of children having their breathing muscles paralyzed and being put into boxes, iron lungs, and trying to keep them alive. That's a crazy change.

Jacob Trefethen:
A crazy change, and hopefully one day soon we'll get rid of the last remaining polio cases.

Saloni Dattani:
The next one, which I think we can end on, is the measles vaccine.

Jacob Trefethen:
Another virus.

Saloni Dattani:
Another virus. I think I didn't really know very much about how bad measles was until I was reading about it for an article I wrote a few months ago. The thing that I didn't know was: measles basically infects your immune cells, so it infects memory T and B cells, which usually help your immune system recognize past infections. But now, instead of being able to fight the virus, the virus uses those cells to transport itself into your bloodstream and get into different cells in your body.

It uses them to spread into your spleen and bone marrow and digestive tract and kidneys and liver. Then you can develop lots of complications from it replicating in those tissues, in those organs, and causes lots of different complications, like ear infections, pneumonia, diarrhea, dehydration, also potentially blindness and brain swelling.

The fact that it infects those immune cells means that it depletes them by infecting them. That means that you can lose your memory responses to other infections that you've had in the past. If you've developed immunity to other diseases or you've been vaccinated against other diseases, that immunity can actually fade through a measles infection. That was something that I didn't really know very much about before. It's why if you look at children who have had contracted measles, they then have a higher risk of just seeing the doctor for various infectious diseases over the next two to three years, usually, which is quite bad.

So we need to get a vaccine for this. How does it happen? It's by John Enders again. He develops culture techniques, he finds the right cell culture to grow the virus in and then to attenuate it. He and his research group find a school that is having a measles outbreak. He takes samples from lots of those kids. From one of those kids, a 13-year-old boy called David Edmonston, he finds a virus strain that he can grow in the lab, and then he names the strain after the boy. It's called the Edmonston strain.

Jacob Trefethen:
Good! I love that.

Saloni Dattani:
I think it's so cool to have a vaccine that's named after you.

Jacob Trefethen:
Yeah, what would the Saloni vaccine do?

Saloni Dattani:
I don't know... something silly.

So he takes this virus strain from this boy and then grows it in human kidney cells and fertilized chicken eggs. That forces it to adapt and lose its ability to cause disease. He then does vaccine trials in 1960, and that was very effective. But many of the kids developed fevers and rashes and things like that. There were new vaccines and different preparations that doctors were using to make them safer. Eventually, Maurice Hilleman, who developed 40 vaccines in his lifetime, developed the MMR with it. It was measles, mumps, and rubella together. He also developed a better measles vaccine. That meant you could just give them all at once. I think that was introduced in 1971, and kaboom.

Jacob Trefethen:
Kaboom!

Saloni Dattani:
So we have gone from a chance discovery of, it just happens to be the case that cowpox is protecting people from smallpox as well, and it happens to be mild, and it happens to be something you can easily identify and work with. But you have no idea what is causing the disease. You have no idea how to grow it reproducibly in the lab. You don't know how to scale it and you're transferring it from arm to arm.

Over time, all of these different innovations in scaling up the method, but also figuring out the theory of, how do germs cause disease and which germ causes each disease? How do we grow them and study them in the lab? How do we make them safer and how do we make them more effective? Doing that for bacteria, and viruses, and now some parasites, like malaria, has taken a very long time and a lot of different efforts from different people, including all the people that we talked about so far.

Jacob Trefethen:
We are ending this episode with MMR in 1971. I just wanted to read out all the different vaccines made starting with smallpox and Edward Jenner in 1796 through to MMR. Smallpox, rabies, cholera, typhoid, plague, pertussis, tuberculosis, diphtheria, tetanus, yellow fever, tick-borne encephalitis, anthrax, influenza, Japanese encephalitis, polio, measles, mumps, rubella.

Saloni Dattani:
Boom. So many.

Jacob Trefethen:
So many.

Saloni Dattani:
We're going to talk about the next ones in our next episode and a different type of vaccine technology and how we do modern vaccines today. Because the process has kind of changed for a lot of different vaccines, and I think that deserves its own episode. But this whole progression from moving from not knowing how to develop a vaccine to figuring out these techniques that systematically allow you to make vaccines against different diseases is itself just an amazing set of achievements.

Coming back to your point right at the beginning, in just the last 50 years, it's estimated that vaccines have saved more than 150 million lives. Despite the false starts and the hundreds of experiments and sometimes grisly methods, people managed to find ways to develop vaccines against so many diseases. They found ways to make them safer and more effective and found ways to scale them up, and you know, I think that's amazing.

Jacob Trefethen:
It sure is. Before we get to those achievements, I just feel grateful for all the scientists all those generations ago, and all of their beefs and all of their feuds. I even feel grateful for Louis Pasteur, even Louis Pasteur. My favorite of everyone we mentioned today is probably that kid, Edmonston, he seemed like a good one.

Saloni Dattani:
He is good. Yeah. Who's my favorite? My favorite is the wife of Robert Koch's assistant, Fanny Hesse. She's like, why don't you use agar? That's not going to melt in the summer. Maybe John Enders as well, the fact that he just happened to move into microbiology from studying languages before... could be an inspiration to some of you in the audience right now. Just kidding.

Jacob Trefethen:
Not kidding. Buckle up. Back to school!

Saloni Dattani:
All right, so we have now reached the end of the episode. I hope you share this with everyone you know. Subscribe, rate this on Apple, Spotify, wherever you get your podcasts, and tell everyone about it.

Jacob Trefethen:
Yes, please do. The ratings actually really help us find new audience, and we have a lot of fun making this. Thanks for lasting all the way to the end with us, and we look forward to talking to you next time.

Saloni Dattani:
Bye-bye.

Jacob Trefethen:
Bye.