Definition
A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. It typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or its surface proteins. Vaccines stimulate the body's immune system to recognize the agent as a threat, destroy it, and keep a record of it, so that the immune system can more easily recognize and destroy any of these microorganisms that it later encounters. Vaccination is a highly effective method of preventing infectious diseases. It's like giving your immune system a training manual for fighting off specific enemies. This preparation can prevent or ameliorate infection upon subsequent exposure to the disease.