A vaccine is a biological preparation designed to elicit immunity and thereby protect the body against an invading microorganism and the particular disease it causes.
A vaccine typically contains one or several molecules that resemble the components of a disease-causing microorganism, such as its toxins or the surface proteins its uses to infect human cells. A vaccine can also be made from weakened or killed forms of a microbe. A vaccine stimulates and educates the body’s immune system to recognize the original microbe as a threat, to attack it and to destroy it. Since the immune system can maintain its memory, vaccines can also train the immune system to recognize and destroy the target microorganism in the future, thus prevent infections for a long period of time or even for life.