By the 18th century, smallpox inoculations were still dangerous and of limited efficiency. Jenner hypothesized that infection with cowpox, a disease non-lethal to humans, granted immunity to smallpox. His theory was confirmed when in 1796, he experimented by infecting a young boy with cowpox and then smallpox. Despite the success of his test, with no undue harm inflicted on the boy, the medical establishment disapproved of his method as he had risked the life of the boy without his consent. Thus, cowpox-based vaccination only saw widespread use sometime after 1800.
- Assassin's Creed III (mentioned only)