Explanation:

 Here's how vaccines work:
• Most vaccines contain a little bit of a disease germ that is weak or dead. Vaccines do NOT contain the type of germ that makes you sick. Some vaccines do not contain any germs.
• Having this little bit of the germ inside your body makes your body's defence system build antibodies to fight off this kind of germ. Antibodies help trap and kill germs that could lead to disease.
• Your body can make antibodies in two ways: by getting the disease or by getting the vaccine. Getting the vaccine is a much safer way to make antibodies without having the suffering of the disease itself and the risk of becoming disabled or even dying.
• Antibodies stay with you for a long time. They remember how to fight off the germ. If the real germ that causes this disease (not the vaccine) enters your body in the future, your defence system knows how to fight it off.
• Often, your defence system will remember how to fight a germ for the rest of your life. Sometimes, your defence system needs a booster shot to remind it how to fight off this germ.
Sometimes vaccines prevent one disease. Sometimes they are combined to protect you from several diseases with one shot. For example, the MMR vaccine fights Measles, Mumps and Rubella (German measles).