Edward Jenner used cowpox in 1796 to protect a boy from smallpox.
Jenner was an English physician who investigated the rural observation that milkmaids who had caught cowpox often appeared protected from smallpox. On May 14, 1796, he inoculated eight-year-old James Phipps with material taken from cowpox lesions on the hand of milkmaid Sarah Nelmes.
Jenner later tested whether Phipps was susceptible to smallpox and reported that the boy did not develop the disease. By modern standards, the procedure would violate research protections for children, but it became a landmark in the history of immunization.
The word “vaccine” comes from the Latin vacca, meaning cow. Vaccination eventually replaced variolation, an older practice that deliberately exposed people to smallpox material but carried a significant risk of severe disease.