The first successful vaccine, developed against smallpox, was created in 1796 by Edward Jenner. Jenner discovered that exposure to cowpox, a less severe disease, provided immunity to smallpox, a deadly and contagious disease prevalent at the time. He conducted an experiment by inoculating a young boy with cowpox and later exposing him to smallpox, demonstrating that the boy did not contract the disease. Jenner's work laid the foundation for immunology and vaccination, leading to widespread efforts to eradicate smallpox. This achievement marked a significant advancement in public health, ultimately contributing to the complete eradication of smallpox by 1980.