A vaccine is an antigenic preparation used to produce active immunity to a disease, in order to prevent or ameliorate the effects of infection by any natural or "wild" strain of the organism. The term derives from Edward Jenner's use of cowpox ("vacca" means cow in Latin), which, when administered to humans, provided them protection against smallpox, which Pasteur and others perpetuated. The process of distributing and administrating vaccines is referred to as vaccination.

Vaccines against cancer are also being investigated; see cancer vaccine. In this case, the antigenic preparation is derived from the cancer cell. There is also research on an HIV vaccine.

Origin of vaccines