Applied Microbiology

A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine 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 one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as foreign, destroy it, and "remember" it, so that the immune system can more easily recognize and destroy any of these microorganisms that it later encounters. Vaccines "teach" your body how to defend itself when germs, such as viruses or bacteria, invade it, they expose you to a very small, very safe amount of viruses or bacteria that have been weakened or killed. Your immune system then learns to recognize and attack the infection if you are exposed to it later in life. This is a natural way to deal with infectious diseases.