ne noun vac·​cine | \ vak-ˈsēn, ˈvak-ˌ
Medical Definition of vaccine 1: matter or a preparation containing the virus of cowpox used to vaccinate a person against smallpox 2: a preparation that is administered (as by injection) to stimulate the body's immune response against a specific infectious disease: a: an antigenic preparation of a typically inactivated or attenuated pathogenic agent (such as a bacterium or virus) or one of its components or products (such as a protein or toxin) b: a preparation of genetic material (such as a strand of synthesized messenger RNA) that is used by the cells of the body to produce an antigenic substance (such as a fragment of virus spike protein)