Vaccines contain a minimal trace of the same germs that cause the disease that they are designed to immunize you from acquiring. For example, if you are getting a measles vaccine, the vaccine will contain a tiny amount of the measles virus. While this aspect of vaccines may seem counterintuitive, the amount of the virus in the vaccine is controlled so that your body will be able to produce the antibodies needed to kill the virus. The amount of the virus in the vaccine will either be weakened or killed so that you don’t get sick. After the vaccine, your immune system will remember the structure of the virus, so that if it ever enters your body in the future, your immune system will be able to react quick enough to kill it before you get sick from the virus. In this way, vaccines provide you with immunity from a disease without your having to get sick from it first!