1. A suspension of deactivated, or killed microorganisms, (bacteria, viruses, or rickettsiae), or of antigenic proteins derived from them, administered for the prevention, amelioration, or treatment of infectious diseases.
2. Etymology: derived from, pertaining to, or relating to, cows. From Latin vaccinus "pertaining to cows", from vacca, "cow" (from the use of cowpox virus inoculation for immunization against smallpox).

Appearing in, characteristic of, the disease of cow-pox.

A material which can either be live, but weakened forms of pathogens; such as, bacteria or viruses, killed or inactivated forms of these pathogens; or purified material; such as, proteins.