A vaccine is a way to develop the natural immunity of the body that prevents us from getting sick. Vaccines are made up of weak bacteria and virus responsible for the disease. Few vaccines are also prepared using dead organisms that were killed to preserve their ability to prevent infection. When the vaccine is introduced into the body, the immune system detects and reacts to the germs in a similar manner as it would if an actual infection arise. It starts making antibodies against the vaccinated germs. These antibodies remain in the body and work against actual infections.