Health Library

Vaccines (or immunizations) are carefully tested to make sure they’re safe for everyone. Even after vaccines are approved, experts keep watching them to make sure they stay safe. Learn why millions of people trust them to help protect people from serious diseases.

How Are Vaccines Studied and Improved?

Before a new vaccine is used, it goes through many tests in labs and with volunteers. The American Academy of Pediatrics recommends vaccines that the Food and Drug Administration (FDA) has approved and says should be in the vaccine schedule. Even after this, experts keep checking vaccines to make sure they stay safe. Over time, vaccines are improved to help lower side effects and meet the highest safety standards.

What Side Effects Can Happen From Vaccines?

The most common reactions to vaccines are minor and may include fever or redness, swelling, and soreness where the shot was given.

In rare cases, vaccines can trigger a serious problem, like a severe allergic reaction. If your child has allergies to food or medicine, or has had a problem with a vaccine before, tell the doctor before your child gets any vaccines. Each year, millions of kids are safely vaccinated and very few have serious side effects.

Do Vaccines or Thimerosal Cause Autism?

No. There’s no link between vaccines and autism spectrum disorder.

Thimerosal (a substance used since the 1930s to help keep vaccines fresh and safe) does not cause autism, either. Studies show that babies who got vaccines with thimerosal didn’t have problems with learning or behavior. Today, routine vaccines for babies and young children have no thimerosal. Some flu vaccines have small amounts of thimerosal, which has been found to be safe.

Do Vaccines Cause SIDS, Multiple Sclerosis, or Other Problems?

Studies have not shown any link between vaccines and sudden infant death syndrome (SIDS), a condition called multiple sclerosis, or other problems. In fact, the number of SIDS cases dropped after doctors first recommended putting babies to sleep on their backs — even though the number of vaccines given yearly was rising at that time.

Can a Vaccine Give Someone the Disease It’s Supposed to Prevent?

Most vaccines contain either a dead or weakened germ (or parts of it) that causes a certain disease. You can’t get sick from vaccines made with dead germs or just parts of the germs. These vaccines can’t cause the disease they’re made to help prevent.

Some vaccines are made with live germs that are very weak, or attenuated, like the chickenpox (varicella) and measles-mumps-rubella (MMR) vaccines. They might cause a mild form of the illness they’re made to help prevent, but it’s much less serious than getting the full disease. Kids with weak immune systems, like those getting treated for cancer, might need to wait to get these types of vaccines.

One live virus vaccine, oral polio vaccine (OPV), is no longer used in the United States. OPV can be found in the spit and poop of people who got the vaccine and can then spread to others. The success of the polio vaccination program made it possible to replace OPV with the inactivated polio vaccine (IPV), which contains a killed virus. This change means that vaccinated U.S. children can’t spread polio disease. OPV is still used in many other countries, though, with great success in reducing the number of cases worldwide.

Where Can I Learn More About Vaccines?

Read about your child’s vaccines for details about each one that’s recommended. The American Academy of Pediatrics also has more information about vaccines.

And talk with your doctor about which vaccines your child needs. Working together, you can help keep your family healthy.

Other Common Questions

Can My Child Get Vaccines While Taking Antibiotics?

If kids are taking antibiotics for a mild illness, they can usually still get their vaccines. Learn when it’s safe to vaccinate and when to wait.

When Is It Too Late to Get the Flu Vaccine?

It’s best to get the flu vaccine early in flu season, so the body can start working to protect itself from the flu. Find out why getting the flu vaccine later is better than not getting it at all.

When Should Kids With IBD Get Vaccines?

Kids with inflammatory bowel disease (IBD) should get their vaccines on the same schedule as other children, with just a few differences if they take certain medicines. Find out more about vaccines and IBD.