The first successful vaccine, developed by Edward Jenner, was introduced in 1796. Jenner used the cowpox virus to create immunity against smallpox, a deadly disease that plagued populations for centuries. His pioneering work laid the foundation for immunology and vaccination, ultimately leading to the global efforts that eradicated smallpox in 1980. Jenner's method demonstrated how exposing a person to a weaker strain of a virus could protect against the more virulent form, revolutionizing medicine and public health. This breakthrough has since paved the way for the development of numerous vaccines against various infectious diseases.