Edward Jenner
After 1770, at least five investigators in England and Germany (Sevel, Jensen, Jesty 1774, Rendell, Plett 1791) successfully tested a cowpox vaccine in humans against smallpox. For example, Dorset farmer Benjamin Jesty successfully vaccinated and presumably induced immunity with cowpox in his wife and two children during a smallpox epidemic in 1774. Jenner may have been aware of Jesty's procedures and success, but after Jenner's work some 20 years later the procedure became widely understood at last.