-An injection of dead, weakened, or modified pathogens into the body. Their presence in the body activates the immune system, which responds to the substances within the vaccine the same way it responds to any other infection: by activating lymphocytes, producing antibodies, and then remembering that disease for a very long time so you don’t get it again. Antigens in the material contained in the vaccine cause the body to produce antibodies. A specialized type of lymphocyte referred to as a memory cell will remain long after the “infection” is cleared out, and will be able to rapidly produce antibodies when you are exposed to the true infection, thus keeping you from ever getting sick. Vaccinations have been used to reduce the incidence of several types of disease. It has eliminated smallpox and polio, in this country and many others; it keeps us from getting the flu; it is even used to protect us from certain types of cancer, such as HPV.