When a virus enters your body, your body has to recognize it, then produce a protein called an antibody. These antibodies attach to the virus and neutralize it; however, in the time it takes your body to produce enough antibodies, the virus may have already multiplied enough to make you sick. Here’s the good news once your body has learned to make the right antibodies, it can make them much faster, neutralizing the virus before you get sick. Vaccines teach your body to recognize and react to a virus quickly. There are two types of vaccines you can get to teach your body to recognize a virus. Inactivated vaccines contain a dead virus, which cannot infect your cells, but your body recognizes it as a virus and produces antibodies to neutralize it. The vaccines for polio and the seasonal flu use dead viruses.