In the world of virology, the nomenclature of war comes easy. The human body is a citadel that relies on the immune system to defend it. A virus is an attacking army that does everything it can to overrun those defenses. Vaccines help. Though they do not prevent the virus from causing an infection, they can control the infection before it leads to symptoms and disease. By staging a scrimmage against the immune system, vaccines teach the body to enlist and train a specialized force of white blood cells and antibodies that are called up in the event of a life-threatening attack.