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Safety & Prevention

How Vaccines for Children & Teens Work

Baby getting a checkup Baby getting a checkup

Have you ever wondered how a tiny shot can keep a baby from getting a serious disease? When they are born, babies have immunity to some diseases passed on to them by their mother. But the immunity does not last or protect babies from all vaccine-preventable diseases.

The good news is that we have many safe vaccines that work well to protect babies and kids when they need it. They are included in the Recommended Childhood and Adolescent Immunization Schedule for ages 18 Years or Younger. Each year, experts, including pediatricians, review the most recent scientific data for each vaccine before approving the schedule.

Vaccines work in a few different ways

Vaccines are like teachers. They teach your child's immune system to protect us from deadly diseases. When your child gets a vaccine, the immune system gets to work right away. It takes what it learned from the vaccine so it can be ready if your child is exposed to harmful germs.

All of us are exposed to germs every day. Some might cause a cold or a minor illness. But then there are more dangerous viruses and bacteria that can make children very sick. Diseases like measles, diphtheria and polio used to sicken and kill thousands of children. That's why it's important to get vaccinated—so your immune system will know what to do.

Vaccination or immunization: What's the difference?
The words vaccination and immunization often are used to mean the same thing. Vaccination is the act of introducing a vaccine into the body (usually as a shot) to produce protection from a disease. Immunization is the process of getting protected from a disease by being vaccinated. Because of continued and widespread immunization, diseases that used to be deadly for children are very rare now.

Take a closer look

Vaccines contain either an antigen—a piece of the germ—or some instructions that tell us how to make the antigen. They teach your immune system to produce antibodies to get rid of the virus or bacteria. Then, those antibodies remember what to do if your child is exposed in the future.

In some vaccines, the antigen is a virus that has been weakened. This means it will not be able to reproduce in your body to make you sick. But it does a great job of teaching your immune system to be ready for the real thing in the future.

Other vaccines use a virus that has been killed, a tiny piece of a virus or bacteria, or a weakened form of a toxin, like the kind produced by the bacteria that cause diphtheria and tetanus. It can't make you sick, but it teaches your immune system to recognize the germ. Getting one or more doses of a vaccine later on gives the immune system a memory boost so it remembers what to do.


The recipe for most vaccines is pretty simple. Besides the antigen, some vaccines contain aluminum salts. This helps make the antigen work better so children can get a lower dose. The amount of aluminum in vaccines is small—much less than your child gets from everyday food and water. Some vaccines also include a preservative to keep germs out and tiny amounts of other ingredients.

That's it! After your child gets a vaccine, their arm may feel sore or they may get a fever. That's a sign your child's immune system is getting stronger. After the vaccine does its job, it leaves the body and is gone. A week or two later your child's immune system is better able to protect your child.


Vaccines have been given to millions of children and teens. They are closely studied and we know they are safe and effective. In fact, vaccines work so well that most reduce your child's risk of getting these diseases by 90 percent or more! It's an amazing way to protect your child so they can stay healthy and safe.

More information

Last Updated
American Academy of Pediatrics (Copyright © 2022)
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
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