The smallpox vaccine is the first vaccine to have been developed against a contagious disease. In 1796, British physician Edward Jenner demonstrated that infection with the relatively mild cowpox virus conferred immunity against the deadly smallpox virus. As the oldest vaccine, the smallpox vaccine has gone through several generations of medical technology. From 1796 to the 1880s, the vaccine was transmitted from one person to another through arm-to-arm vaccination.

Source: Wikipedia