The first successful vaccine for smallpox was invented by Edward Jenner in 1796. Jenner’s pioneering work involved using material from cowpox lesions to inoculate individuals, which provided immunity against smallpox. His experimentation demonstrated that exposure to cowpox could protect against the more deadly smallpox virus. This groundbreaking discovery not only paved the way for the development of immunology but also laid the foundation for vaccination practices still in use today. Jenner's work significantly contributed to the eventual eradication of smallpox, declared by the World Health Organization in 1980.