Pathogen-derived preparation that provides acquired immunity to an infectious disease
A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. A vaccine typically contains a biological preparation from disease-causing microorganism, or since the beginning of the 21st century, made synthetically that resembles it. This preparation is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat and starts producing antibodies against it, so as to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future. Vaccines can be prophylactic, or therapeutic.