Cows, Smallpox an 8 year old boy, and what we did before vaccines
Spare a thought for James Phipps. In the middle of the 18th century when 20% of the worlds population was dying from smallpox, and half of those who survived were left blind or disfigured, a chap called Jenner noticed that milkmaids seems to be immune from smallpox, and guessed that getting a mild dose of cowpox made you immune to deadly small pox. So James (8) was smeared with pus from a build on the arm of a milkmaid and put into a cut in James's arm. (I don't think that would be acceptable nowadays). Anyway James survived the cowpox "inoculation". So two months later James was further abused by being injected with the more deadly smallpox. He failed to develop symptoms and the rest is history. Smallpox was eradicated in 1977.
Before the 18th century humans practised "variolation" - basically exposing yourself to small quantities of the smallpox by breathing in dried pus. (yuck) It was thought that by introducing a milder form of smallpox, you would avoid more serious case. Results were mixed, and there were deaths from the practice and it was observed that even "variolated" people could spread the disease. So in steps another mathematician - Bernoulli (not Scottish) who worked with Edmund Halley of Halley's Comet fame, to develop a "life table" that showed unequivocally the power of medical intervention. However, as we know anti- vaxxers don't believe science or maths and prefer myths.
Jumping ahead to the end of the 19th century plague hit India - thought to have come for Hong Kong via rats carrying the "Yerstina pests" virus. The Indian government practised containment as pandemic control of the outbreak but it nevertheless stayed in the community for decades, eventually killing 12 million people. It was in India that a certain Dr Andrew McKendrick carried out his research and showed that bacteria increased to a carrying capacity according to a logistic growth model (SIR) that led to greater understanding of zoonotic diseases and public health intervention outcomes.
McKendrick was was able to accurately recreate the rise and fall of the plague in the 1905 Bombay outbreak, and the impacts of interventions such as containment, vaccination etc. and so gave public health officials the tools for humans to predict and manage pandemics.