The name of the first successful vaccine developed by Edward Jenner is the smallpox vaccine. In 1796, Jenner observed that milkmaids who had contracted cowpox, a disease similar to smallpox, did not get sick from smallpox. He hypothesized that exposure to cowpox conferred immunity to smallpox. Jenner tested this theory by inoculating a young boy with cowpox, and later exposing him to smallpox, which confirmed his theory of vaccination. This groundbreaking work laid the foundation for the field of immunology and has had a lasting impact on public health, leading to the eventual eradication of smallpox worldwide.