Edward Jenner introduced the first widely used vaccine against smallpox.
In 1796, the English physician tested the idea that infection with cowpox could protect people from smallpox, a far more dangerous disease. On May 14, he inoculated eight-year-old James Phipps with material from a cowpox sore and later demonstrated that the boy resisted smallpox exposure.
Jenner’s work built on earlier practices. Variolation, which deliberately exposed people to smallpox material, had been used in parts of Asia and the Middle East before spreading more widely. It could provide protection, but it also carried the risk of severe disease and transmission. Cowpox vaccination was much safer.
Jenner was not the first person to notice the relationship between cowpox and smallpox; earlier investigators, including Benjamin Jesty, had experimented with it. Jenner’s contribution was to investigate, document, and promote the method so it became widely understood and adopted. The word “vaccine” comes from vaccinia, associated with cowpox.