The first successful vaccine was developed by Edward Jenner in 1796. Jenner, an English physician, discovered that milkmaids who contracted cowpox did not get smallpox, leading him to hypothesize that cowpox could be used to protect against the more deadly smallpox. He conducted an experiment by inoculating James Phipps, a young boy, with cowpox and later exposing him to smallpox. The boy did not develop the disease, proving the efficacy of the vaccine. This pioneering work laid the foundation for immunology and the development of vaccines that have since eradicated or controlled numerous infectious diseases.