Vaccines are made from the same germs (or parts of them) that cause disease. Measles vaccine is made from measles virus, for instance, and Haemophilus influenzae type B (Hib) vaccine is made from parts of the Hib bacteria. But the germs in vaccines are either killed or weakened so they won't make you sick. Then the vaccines containing these weakened or killed germs are introduced into your body, usually by injection. Your immune system reacts to the vaccine the same as it would if it were being invaded by the disease -- by making antibodies. The antibodies destroy the vaccine germs just as they would the disease germs. Then they stay in your body, giving you immunity. If you are ever exposed to the real disease, the antibodies will be there to protect you.
Immunizations help your child's immune system do its work. The child develops protection against future infections, the same as if he or she had been exposed to the natural disease. The good news is, with vaccines your child doesn't have to get sick first to get that protection.
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