A vaccine is designed to produce protection in the body from disease. It does this by allowing the body's immune system to make antibodies to protect itself against invading germs. These antibodies act together with other cells in a coordinated way to destroy the offending micro-organism and cells that have been infected.

A vaccine is usually a weakened or killed version of the infecting germ. It is licensed and given to humans only after years of intensive research to test its safety and efficacy (whether it elicits the desired protection against the disease) on both animals and human subjects.

The most common method of administering vaccines is by injection into the skin or muscle, but some vaccines are given by mouth or nasal spray.