The first successful vaccine developed for smallpox was created by Edward Jenner in 1796. Jenner, an English physician, discovered that milkmaids who had contracted cowpox, a disease similar to smallpox but less severe, appeared to be immune to smallpox. He hypothesized that exposure to a less virulent pathogen could confer immunity to a more deadly one. Jenner tested his theory by inoculating a young boy with cowpox and subsequently exposing him to smallpox; the boy did not contract the disease. Jenner's work laid the foundation for the field of immunology and vaccination, ultimately leading to the eradication of smallpox in 1980.