Real Dictionary

vaccine
variable noun: A vaccine is a substance containing a harmless form of the germs that cause a particular disease. It is given to people, usually by injection, to prevent them getting that disease.

vaccine in American English
lymph, or a preparation of this, from a cowpox vesicle, containing the causative virus and used in vaccination against cowpox or smallpox
of cowpox or vaccination
adjective: of or pertaining to vaccination
noun: any preparation used as a preventive inoculation to confer immunity against a specific disease, usually employing an innocuous form of the disease agent, as killed or weakened bacteria or viruses, to stimulate antibody production

vaccine in British English
noun: a suspension of dead, attenuated, or otherwise modified microorganisms (viruses, bacteria, or rickettsiae) for inoculation to produce immunity to a disease by stimulating the production of antibodies