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James Gillray, The Cow-Pock—or—the Wonderful Effects of the New Inoculation! (1802). Vaccinations eventually helped eliminate smallpox from the world.

A modern kit to vaccinate against smallpox

A vaccine is a biological preparation. It is given to prevent a specific infectious or malignant disease. It only works against the microorganism for which it is prepared. It is usually given by injection, and called vaccination.

At its best, vaccination gives immunity to an infectious disease caused by a particular microorganism (bacteria or virus). For example, the flu vaccine makes it very much less likely that a person will get the flu. The flu virus continually changes, and has many strains. That is why re-vaccination is needed every year.