Vaccines (also known as immunizations) 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 will make 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.
Although getting a vaccine may not completely prevent you from getting a disease, it does make it much less likely. And if you get a disease even after you have been vaccinated, it usually will be only a mild case.