Vaccines help prevent people from getting sick. They also help reduce the spread of disease to others and prevent epidemics. There are many kinds of vaccines. Each vaccine is made up of parts of weakened or killed bacteria or viruses of a specific disease. After you have a vaccine, your body's immune system makes antibodies to fight the disease. If you are exposed to the same disease in the future, the antibodies kill the bacteria or viruses before they have a chance to make you sick.
If you get a vaccine, it may not completely prevent you from getting a disease, but it makes it much less likely. If you get a disease even after you have been vaccinated, it usually will be only a mild case.