SYMHC Classics: Eradication of Smallpox
Stuff You Missed in History Class
This episode explores the global effort that led to the eradication of smallpox, one of only two diseases ever eliminated through human acti
Key takeaways
- Smallpox was uniquely suited for eradication due to its high visibility, exclusive human transmission, and lifelong immunity after recovery.
Main topics
- History of smallpox
- Development of the smallpox vaccine
Notable quotes
Smallpox was finally eradicated. It does still exist in a couple of labs.
Conclusion
Smallpox stands as a landmark achievement in public health, demonstrating
Transcript preview
Speaker 1 (0:00) This is an iHeart Podcast. Guaranteed human. Speaker 2 (0:06) Happy Saturday. Since we mentioned our episode on the eradication of smallpox this week, we are bringing it out as today's Saturday classic. At Speaker 1 (0:15) the end of this episode, we mentioned guinea worm disease, also called draconchioliasis, as a disease that could potentially be eradicated. According to the World Health Organization, in 2025, there were 10 reported cases of draconchioliasis. There were 15 in 2024. 14 in 2023, and 13 in 2022. This Speaker 2 (0:38) episode originally came out September 1st, 2021. Enjoy! Speaker 1 (0:45) Welcome to Stuff You Missed in History Class, a production of iHeartRadio. Speaker 2 (0:55) Hello and welcome to the podcast. I'm Tracy B. Wilson. And I'm Holly Frey. Late March of last year, I researched and wrote our episode on the eradication of render pests. Because in that moment, it just felt really weird to me to work on episodes that were not about the pandemic somehow. Because that was dominating everything in our lives. But at the same time, I wanted to work on something that felt kind of optimistic because the pandemic was dominating our lives. So now it's almost a year and a half later. Here in the U.S., we had a pretty hopeful springtime regarding the progress of the pandemic. I know that was not the case in the whole world, but we had what was looking like... improved situations. That obviously has taken a turn once again for the worst, or at least the worst, maybe not the worst of ever, but definitely worse. I wanted to kind of return to the idea of wiping a disease off the face of the earth. So, rinderpest and smallpox are the only two diseases that have been eradicated through human activity. Neither one of them is technically extinct because there are some samples of both viruses that still exist in labs. They're no longer circulating out in the wild, though. And we've talked about smallpox a bit on the show before. We had our episode on Edward Jenner and the smallpox vaccine and how the vaccine was developed and then Jenner's efforts to try to make it more widely available. More recently... We did the episode on the Royal Philanthropic Vaccine Expedition, and that was all about Spain's efforts to transport the smallpox vaccine to the Americas, which required a chain of living human hosts. We mentioned, pretty briefly, the eradication of smallpox in both of those episodes, but we have not gone into detail about how that happened. That's what we're going to talk about today. Speaker 2 (2:59) When Tracy Speaker 1 (3:00) mentioned it to me, I said, we've covered that. No, Speaker 2 (3:02) it just keeps Speaker 1 (3:03) coming up. It just keeps coming up. Speaker 2 (3:05) We've said in like a sentence how it was done, but it's a more than a sentence worth of explanation. Speaker 1 (3:11) Yeah, it's been just peppered in enough that my brain was like, yeah, that was an episode, right? Nope. Nope. So smallpox is a viral disease that has existed for millennia. When it was circulating in the wild, it spread from person to person through the air, usually through face-to-face contact, and it can also be spread through contact with contaminated objects and surfaces. People who contracted smallpox typically developed a high fever and body aches, and that was followed by a distinctive rash. There Speaker 2 (3:44) are two different strains of the variola virus that were causing smallpox, variola major and variola minor. As that name suggests, variola major caused more serious illnesses. As many as a third of people who were infected with variola major died. As many as 90 % of babies died. It was also particularly lethal any time it was introduced somewhere that it hadn't existed before, such as when Europeans started arriving in the Americas. And in those cases, smallpox usually killed about half the people who contracted it. Among the people who survived the disease, smallpox could also be both disabling and disfiguring. Speaker 1 (4:25) There was, and is, no cure for smallpox, so even as science and medicine progressed, it continued to be deadly. But it also had some traits that made it a good candidate for a worldwide eradication campaign. Smallpox was easy to recognize and diagnose, unlike, say, the flu, which can resemble a lot of other respiratory infections. Smallpox passed directly from person to person and only infected humans, so there were no hidden reservoirs of the virus that could potentially start a new outbreak. That's different from something like yellow fever, which also infects other primates and is transmitted by mosquitoes. Another plus, once a person had recovered from smallpox, they were immune for life. Speaker 2 (5:11) For Speaker 1 (5:12) a number Speaker 2 (5:12) of reasons, smallpox outbreaks also tended to develop relatively slowly. Once people were contagious, they were usually also too sick to really leave home. So outbreaks tended to cluster around members of the same household and their immediate neighborhood. And then once an outbreak was identified, swift action could keep it from spreading very far. Speaker 1 (5:34) And most importantly, there was a way to disrupt transmission of the disease, in this case, a vaccine. In terms of the smallpox vaccine, at first, people prevented smallpox using a technique called variolation that involved intentionally introducing material from one person's smallpox sore or scab into another person. Practitioners in Asia were doing this as early as the 11th century, and the technique spread from there. Then, in the late 18th century, people started to make a connection between smallpox and another much milder disease that was called cowpox. The smallpox and cowpox viruses are both in the genus Orthopoxvirus, and people who had contracted cowpox seemed immune to smallpox. Several people, including Edward Jenner, tried deliberately exposing people to cowpox. as a way to prevent smallpox. Jenner called this vaccination after the Latin word for cow. So Speaker 2 (6:32) both variolation and vaccination could prevent smallpox. But since variolation could also cause full-blown smallpox, vaccination was a lot safer. At the same time, though, vaccination in its earliest forms carried some of the same risks that variolation did, including the potential for transmitting other illnesses like syphilis and hepatitis from person to person during these person-to-person vaccination chains. Speaker 1 (7:00) Sometime in the 19th century, people shifted from using cowpox to using vaccinia virus, which is another orthopox virus, to make smallpox vaccine. The origins of the vaccinia virus are unclear. It is possible that it's actually some kind of hybrid of cowpox and smallpox, or that it developed over time as cowpox virus was passed through multiple hosts in the process of making vaccines. Eventually, vaccinia virus replaced cowpox virus for vaccination purposes, just as vaccination with cowpox had previously replaced variolation with smallpox itself. Speaker 2 (7:39) At first, vaccines made with vaccinia virus were grown in the skin of live animals like calves, sheep, and rabbits. Eventually, that shifted to growing the virus in tissue cultures or in chicken eggs. These methods replaced those arm-to-arm vaccination chains that we talked about in our episode on the Royal Philanthropic Vaccine Expedition. Countries actually started to outlaw arm-to-arm vaccinations in the late 19th century. Speaker 1 (8:06) Many of the vaccinia strains used to make vaccines were attenuated or weakened by repeatedly passing them through a non-human host. Things like chick embryo cells, eggs, or mice. This process resulted in a virus that produced an immune response when a person was vaccinated with it, but couldn't reproduce in that person's body and make them sick. So while vaccination with cowpox virus was safer than variolation with smallpox virus, Vaccination with an attenuated version of vaccinia virus was also safer than vaccination with live, unattenuated cowpox. Yeah, Speaker 2 (8:43) there were still potentials for various complications, but this was an improvement overall. It really didn't take long after the development of vaccines for people to wonder whether vaccines could be used to eliminate smallpox entirely. But early attempts to do this faced a lot of obstacles. As we talked about in our episode on the Royal Philanthropic Vaccine Expedition, early versions of smallpox vaccine lost their potency really quickly, especially in hot weather. And that continued to be true after vaccinia replaced cowpox as the preferred virus for smallpox vaccines. Speaker 1 (9:21) But then in the 1940s, people started working on dehydrated and freeze-dried versions of the vaccine. The Vaccine Institute in Paris produced a freeze-dried, vacuum-packed vaccine that had a longer shelf life. In the 1950s, Leslie Harold Collier at the Lister Institute studied the preservation methods that were in use and how effective they were, and he developed a process that didn't require refrigeration, even in tropical temperatures. Once the vaccine was reconstituted, it still had a short shelf life, but until that point, it could survive in the field for months. It also protected people from smallpox infection for at least 10 years and offered protection against dying of smallpox for some time after that. Collier's method eventually became the World Health Organization standard for vaccine used for the eradication campaign. Speaker 2 (10:13) Smallpox was eliminated in North America in 1952 and in Europe in 1953. And that was done primarily through mass vaccination campaigns, especially ones that were done in response to outbreaks. And this success came in spite of increasing resistance to vaccines and to compulsory vaccine programs. In the United States, this resistance led to a Supreme Court case in 1905. The city of Cambridge, Massachusetts, had been trying to stop a smallpox outbreak and had ordered all adults to be vaccinated or to pay a $5 fine. Henning Jacobson refused to be vaccinated, and then after being fined, he took the matter to Speaker 1 (10:55)