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Safety & Prevention

Vaccine Risks & Benefits

By: Whitney Casares, MD, MPH, FAAP

Childhood vaccination has been one of modern medicines biggest success stories. In fact, vaccines for children have been so successful that we no longer see many of the diseases that used to cause severe illnesses and lasting disabilities.

Thanks to vaccines, most children will never get whooping cough, tetanus, polio or meningitis—so we rarely see how serious these diseases can be. As a result, parents may wonder if their child needs all of the recommended vaccinations.

Perhaps you've asked yourself this question and Googled it. These days, it's easy to search online for answers that support a belief about risks of vaccines. But the bulk of these claims are inaccurate and unproven. A lot of this information is not just scary—it has caused parents to second-guess the facts they hear from their pediatrician and other trusted sources. And it scares people away from a vaccine that could save their child's life.

The disinformation dozen

You may be surprised to know that the "anti-vaccine" content on social media platforms about kids and vaccines originates from a tiny group of just 12 people. In a 2021 analysis, the Center for Countering Digital Hate found that this tiny group—it nicknamed the "disinformation dozen"—was the original source of about two-thirds of the anti-vaccine posts and messages. These 12 individuals wanted to draw more traffic to their own websites.

Anti-vaccine posts are not fact-checked

Just like other rumors that go viral on social media platforms, these anti-vaccine posts are not checked for accuracy. They may not be the best or most accurate information about your baby's vaccines. Here's what else to keep in mind:

  • Social media algorithms promote posts that are likely to appeal to a lot of people, like ones with the most clicks or followers or posts from celebrities.

  • When you click on or interact with even one false piece of information, the platform will show you more and more similar kinds of content. This can lead you into a disinformation "rabbit hole" without you even realizing it.

  • The posts seem authentic and convincing. That's why they are so effective at influencing parents who are searching for answers to questions about their child's health. These posts spread easily and get shared by tens of thousands of people who may not even know where the post came from.

  • When experts post accurate content, they often get targeted by anti-vaxxers who want to drown out the facts.

Vaccine side effects & myths

For years, people have spread rumors online using a variety of angles, including rumors about vaccines and autism spectrum disorder (ASD), sudden infant death syndrome (SIDS) and developmental delays. Here are a few examples:

Vaccines & autism spectrum disorder (ASD)

In the 1990s, a paper was published by a doctor who looked at 12 kids and theorized that their autism was due to vaccines. Specifically, it looked at the measles-mumps-rubella (MMR) vaccine and a possible link to autism.

Fact: That paper turned out to be based on bad science. It was discredited and the journal retracted it. This single paper caused enough fear among parents that a lot of other studies have been done in many countries and included thousands of children. They found no causal association to link them.

Children with ASD are often diagnosed between 18 and 30 months of age—around the same time the MMR vaccine is given. This has led some people to assume that the vaccine is the cause. Increasing evidence shows that even though the symptoms of ASD may not be visible until the second year after birth or later, ASD starts before a baby is born.

Extensive evidence from the American Academy of Pediatrics (AAP), the Centers for Disease Control and Prevention, the National Academy of Medicine and researchers around the world also have concluded that there is no causal association between the MMR vaccine and autism.

Fears of a possible link between MMR vaccine and autism have led to under-vaccinated areas. Measles has been eliminated in our country since 2000, but the virus still spreads—leading to outbreaks in the United States and around the world.

Thimerosal or mercury & vaccines

A preservative (thimerosal) added to vaccines in the 1930s contains mercury. People feared that this mercury was toxic to humans. Some people thought that it could cause neurologic (nervous system) problems.

Fact: Mercury is a naturally occurring element in the earth's crust, air, soil and water. There are two types of mercury—and they are very different.

Thimerosal contains very small amounts of one type of mercury that is added to some vaccines to prevent germs from growing. This type of mercury does not stay in the body. It is different from the other type of mercury that is found in certain kinds of fish. That type can stay in the human body and make people sick.

Even after many studies, thimerosal has never been shown to cause neurologic problems. Thimerosal has not been used in vaccines for children since 2001. Only some flu vaccines contain thimerosal. If you have any questions or concerns, ask your pediatrician.

Vaccines & SIDS

Babies get many of their first vaccines between 2 and 4 months of age. This is also the peak age for sudden infant death syndrome (SIDS ). Because of the timing, some people feel they might be related.

Fact: Scientific studies have confirmed that vaccines do not cause SIDS. In fact, vaccines may help prevent SIDS. And most importantly to help prevent SIDS, the AAP recommends a safe sleep environment for babies.


When reviewing facts about vaccines for your child, make sure you check the source. Have a high level of suspicion if you don't recognize and trust the original source of the content.

And you can always verify information by going to credible sources like,, the Centers for Disease Control and Prevention website and your child's pediatrician.

More information

About Dr. Casares

Whitney Casares, MD, MPH, FAAP, is a member of the AAP Council on Communications and Media.

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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