Vaccines are biological preparations made from the weakened or killed forms of microbes. They create immunity against a disease. A Traditional vaccine consists of agents that resemble the disease- causing organism. When these agents enter the human body they stimulate the immune system to recognize these agents as foreign and destroy them. It also makes the immune system remember these foreign agents so that they can recognize and destroy the real live virulent germs. A vaccine can be administered into the body through injections, by mouth or by aerosol.