How Humankind Got Ahead of Infectious Disease

With polio on the verge of eradication, a career immunologist explains the medical marvel of vaccination and the pioneers who made it possible

School girls line up to receive vaccinations between classes. (© Paul Chesley/National Geographic Society/Corbis)

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You have to remember that this was taking place when disease was rife, sanitation was poor, there was no reliable supply of clean water so diseases like cholera caused epidemics periodically. Inevitably, that is why people tended to drink beer—small beer it was called, with a low level of alcohol—because they knew it was safe. The standards of life were very much different from what they are today. Any sign of some sort of protective measure was seized upon and the standards of proof were very, very low. If it seemed to be safe, then people would adopt it because they hoped it would be lifesaving. That is how half a dozen prisoners came to persuade King George that this should be adopted for the members of his family.

At what point does Edward Jenner, the English doctor credited as the pioneer of vaccination, come into the picture?

Jenner was aware of variolation that had been championed by the Lady Mary and Princess Caroline, and also in the Americas by Cotton Mather. Jenner himself was variolated as a child; it was a horrendous experience. He was very unwell for quite a while. Part of the reason was that members of the medical profession were trying to regain ownership of the process from practitioners who they viewed as breaking from medical tradition, so they added a period of fasting and strange diet in order to remystify the process. Jenner came across the notion that milkmaids were never susceptible to smallpox, and he realized it might be possible to use an innocuous agent, cowpox, in order to do the same thing as the very dangerous variolation. It took him almost three decades before he actually did the experiments, in the late 1790s. It wasn’t a step in the dark. It was an improvement on something that already existed—a pivotal improvement, which relatively quickly spread across the world.

There are stunning stories of how vaccination spread. Can you offer an example?

The King of Spain and others essentially wanted to protect their colonies, which were enormously valuable assets to them. So, in the early 19th century, in what I’ve called “the founding voyages,” chains of children were vaccinated one by one so that the vaccine remained fresh over the course of a sea voyage. By the end of the voyage, the last few children would be vaccinated so there was fresh material, fresh cowpox material in this case, to begin to vaccinate in South America. The Portuguese also championed the same strategy. One of the good things was they didn’t confine it to their own colonies. They went into Asia as well. And that is how the spread of vaccination occurred across the globe.

Was there a backlash from skeptics?

I don’t think it was anything we would recognize as a legitimate reason to concern over safety. It was much more to do with religious and philosophical objections to the introduction of a bestial humor [a vital fluid from a non-human animal] into the human body. The idea of deliberately using a disease from a cow to protect humans against disease was repugnant to a large group of people. There were more reasoned critics who believed there was little benefit from vaccination, and it took a little while for it to convince people. But it was only a matter of five years or so before it was beginning its inexorable spread.

How did vaccination evolve, and eventually move beyond smallpox?

There was a sort of gradual, slowly evolving incremental improvement until the end of the 19th century. When there was an explosion in the field of bacteriology, scientists began to realize that there were many other diseases which could be addressed with vaccines, and that led to widespread attempts to bring about vaccines for other infectious diseases. Louis Pasteur and Robert Koch were the important figures of the late 19th century.

It was germ theory that altered everything. In the 1860s, Pasteur was first to show that germs do not arise spontaneously. They exist pretty much everywhere around us. He did away with the theory of spontaneous germ generation. He also managed to produce a vaccine against rabies and also cholera. And a lot of his discoveries were almost serendipitous. In the case of cholera, the researchers had left a culture of cholera germ out on the bench, so it grew weak. Then, when they injected it into chickens, instead of getting cholera, the chickens were protected against subsequent infection… Pasteur knew all about Jenner’s work, by the way, and he used the term “vaccine,” extending it to all kinds of vaccines in Jenner’s honor.


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