Today's attempt in this area is an anti-plague vaccine, intended to protect against Yersinia pestis, aka the Black Death or bubonic plague. There were some epidemics going on in India in the early 1900s, and this vaccine apparently did not work well as a treatment for plague, but the author wanted to test its effectiveness as a preventative measure.
In the village of Kirkee at the time, there were two somewhat separate populations: 5,640 civilians and 1,312 people and their families employed by the military. These lived in separate neighborhoods, though the military folk made their purchases at shops in the civilian section. The military folk tended to be poorer, but their huts were more sanitary, and they were more likely to seek (or be required to seek) medical attention for plague symptoms.
So when the epidemic started in Kirkee, 1300 of the 1312 military employees received the vaccine, whereas only 45 of the 5640 civilians were vaccinated.
Of those vaccinated from both sides, 0.37% caught plague (0.38% military and 0% civilian), and 0.0007% died from it (0.0008% military and 0% civilian).
Of those not vaccinated, 6.9% caught plague (50% military, 6.8% civilian), and 4.7% died from it (25% military, 4.6% civilian).
Here's a graph of comparative incidence:
Those do seem like very large differences, but the populations of vaccinated vs. unvaccinated were not nearly equivalent, so it may be difficult to compare.
The vaccine, as those before, was made of bacterial culture killed with heat (and a little carbolic acid, aka phenol), and injected into the arm. Typical side effects were localized pain and swelling within 4 hours, going away after 30 hours. Rare individuals had no reaction or had a localized abscess (probably a secondary infection) that was successfully treated. Doesn't sound too bad, especially if it was an effective protection against the plague.
Citation: Lucas, T. C. A note on Haffkine’s antiplague vaccine. Br Med J 1, 928–929 (1907).
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