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Vaccines and Autism: Is There A Link?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on April 9, 2021.

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What Exactly is Autism, or ASD?

Autism, also known as autism spectrum disorder (ASD), is a brain development disorder in children that leads to problems with communication, behavior, and social interaction. A child may not show signs until age 2 or 3, and symptoms may continue throughout the child’s lifetime.

What exactly causes autism is not known, but most experts agree it is genetically linked. Researchers are also studying whether environmental factors such as viral infections, pregnancy complications, or air pollutants could increase the risk of autism.

ASD is 4 times more common in boys than girls; about 1 out of every 54 children are diagnosed with this disorder, according to the U.S. Centers for Disease and Control (CDC).

There is no known cure for autism, but children can learn new skills.

Are Vaccines Linked to Autism?

The topic of childhood vaccines leading to autism spectrum disorder (ASD) is one that never seems to fades away.

Concerns about vaccines leading to autism surfaced in 1999 and initially involved the measles, mumps and rubella (MMR) vaccine.

Because the MMR vaccine is usually given at age 12 to 15 months, and the first signs of autism often appear at this time, concerns were raised about a link between the MMR vaccine and the development of autism.

The Centers for Disease Control and Prevention (CDC) has conducted 9 studies that have found no association between thimerosal-containing vaccines and ASD, or between the measles, mumps, and rubella (MMR) vaccine and ASD in children.

In 2019, in the largest study ever published on this topic, investigators found no evidence that the measles, mumps and rubella (MMR) vaccine causes autism when looking at over 650,000 Danish children. This result held true even when researchers focused on children at greater risk for developing autism. The results were published in the Annals of Internal Medicine.

Unfortunately researchers are skeptical the new data will change the mind of so-called "anti-vaxxers". However, they feel the large study might provide reassurance to certain parents who are willing to listen to science.

Medical Experts Weight In

In addition, several studies reported by the U.S. Centers for Disease Control and Prevention (CDC) offer assurance to parents that vaccines do not cause autism.

These studies evaluated eight vaccines and also looked at a child's response to antigen development from several vaccines over the first two years of life. Plus, the CDC found that exposure to thimerosal, either early in life or in the womb, does not increase a child’s risk.

Additional studies from Europe, the Institute of Medicine, and the American Academy of Pediatrics have confirmed what the CDC found; the patient advocacy group Autism Speaks also agrees.

Even though the medical evidence strongly supports that vaccines do not cause autism, many parents find the data overwhelming or simply ignore it. Some parents do not follow their child's vaccine schedule and skip immunization, a great cause for concern.

In a study from Kaiser Permanente published in JAMA Pediatrics researchers found evidence that among children aged 4 to 6, those with autism were "significantly less likely" to receive the full range of recommended vaccines compared with other children.

What Started This Concern?

A study published in The Lancet in 1998 (now retracted from publication) stated incorrect findings over an association between the MMR vaccine and autism. Since this time, the majority of the authors and The Lancet have retracted the findings.

In the U.S., many legal cases were brought forth over a supposed link between autism and the MMR vaccine. However, according to the Omnibus Autism Proceeding, it was ruled that the MMR vaccine, either given alone or in conjunction with thimerosal-containing vaccines, was not a causal factor in the development of autism.

Related: Childhood vaccines: Tough questions, straight answers

Is Thimerosal Still Found in Vaccines?

Thimerosal has been removed or reduced to trace amounts in most vaccines, with the exception of the multi-dose vial of the seasonal flu shot. Thimerosal is added to multi-dose vials to help prevent overgrowth of bacteria.

For parents who prefer, preservative-free versions of the flu shot are available; all you have to do is request it from your doctor or pharmacist. You may need to check with your insurance first to be sure they'll pay for the preservative-free form.

Thimerosal used to be found in the hepatitis B, Haemophilus influenzae type B (Hib) and diphtheria, tetanus, and pertussis (DTP) vaccines, among others. The U.S. Food and Drug Administration (FDA) has worked with vaccine manufacturers to eliminate thimerosal from vaccines recommended for children 6 years and younger. In many common childhood vaccines, thimerosol was never present.

Thimerosal is not present in any COVID vaccine issued for emergency use authorization in the U.S. To see a full list of ingredients for COVID-19 vaccines in the U.S., follow this link.

At this time, the only COVID-19 vaccine authorized for use in children is the Pfizer-BioNTech vaccine, and it is only used in children 16 years or older. Studies in younger populations are ongoing.

What Are the Rates of Autism Spectrum Disorder?

Rates of autism are on the rise. However, rates may not be increasing solely because there are more cases of ASD; they might also be increasing due to a broader definition and a better diagnosis of ASD. As the numbers of ASD increase, additional community resources need grow too, such as educational services and a coordinated response to families whose children have ASD.

The CDC has tracked data using the Autism and Developmental Disabilities Monitoring (ADDM) Network Sites. The goals of the ADDM Network are to:

  • Describe the population of children with ASD
  • Compare how common ASD is in different areas of the country
  • Identify changes in ASD occurrence over time
  • Understand the impact of ASD and related conditions in US communities

What Are the Most Common Risk Factors for Autism?

ASD occurs among all racial, ethnic, and socioeconomic groups.

Common risk factors for autism spectrum disorder (ASD) include:

  • Having a twin with ASD, or other family history.
  • Boys are about 4 times more likely to develop ASD than girls.
  • Parents who have had a child with ASD have a 2% to 18% chance of having another child with the disorder.
  • Children born to older parents also seem to have a higher risk, but more research is necessary.
  • About 10% of children with autism also have certain genetic disorders like Rett Syndrome (primarily in girls) or fragile X syndrome, or tuberous sclerosis, where benign tumors develop in the brain.
  • Preterm babies born before 26 weeks of gestation may have an elevated risk of autism spectrum disorder.
  • Over 80% of children diagnosed with ASD also have a psychiatric, neurologic, chromosomal, or genetic diagnosis.

Vaccinations and Herd Immunity

Diseases like polio, whooping cough, measles, Haemophilus influenzae, and diphtheria are becoming very rare in the U.S. because the childhood vaccination programs have worked.

When parents stop vaccinating their child, not only is their child at greater risk of disease, other children in their communities, and other communities, are at elevated risk, too. The benefit from widespread vaccination protecting the larger community is known as herd immunity.

The more people who are vaccinated, the fewer opportunities a disease has to spread. If vaccination rates drop nationally, diseases could become as common as they were before vaccines became available.

For example: smallpox is a true success story; it has been eliminated from the globe since 1980. The last known case of smallpox in the U.S occurred in 1949, and the last case of naturally occurring smallpox was reported in 1977 in Somalia.

Studies are currently ongoing in children to determine the safety and effectiveness of the COVID-19 vaccines in children under 16 years of age, and initial data from Pfizer-BioNTech looks promising. In participants aged 12-15 years old, the Pfizer-BioNTech vaccine demonstrated 100% efficacy and robust antibody responses and was well tolerated. These results exceeded those reported in trial of vaccinated 16-25 year old participants in an earlier analysis.

Currently, the Pfizer-BioNTech vaccine is authorized for use in people 16 years of age and older, but the Moderna and Janssen (J&J) vaccines are only used in adults 18 years and older. Eventual FDA authorization of vaccines for children will help to secure herd immunity for COVID-19 disease worldwide.

What If I Don't Vaccinate My Child?

It is important to vaccinate to prevent outbreaks of diseases that are nearly under control today.

Vaccinations are one of the most important actions we can take to protect ourselves, our children, and our communities from disease. This is especially important for children who cannot be vaccinated because they are too young or sick.

If a case of a disease is introduced into a community where most people are not vaccinated, an outbreak can occur because the widespread protection known as "herd immunity" breaks down. Herd immunity refers to the ability to avoid a contagious disease within a community. This occurs if enough people are immune to the disease by building antibodies, especially through vaccination or prior illness.

In 2000, the United States was declared measles-free.

  • But infected travelers visiting or returning to the US from abroad have caused outbreaks, and unvaccinated children are most at risk, research has shown.
  • As published in the Journal of the American Medical Association (JAMA), several measles outbreaks occurred in the U.S. among groups with low vaccination rates, including in the states of Texas, New York and California, in 2014.
  • As reported by the CDC, from January 1 to December 31, 2019, 1,282 individual cases of measles were confirmed in 31 states in the U.S. The majority of cases were among people who were not vaccinated against measles.

Pertussis (whooping cough) has also been on the rise. Adults may also need to be re-vaccinated against pertussis to protect small babies.

Where Can I Learn More About Autism and Vaccines?

The Centers for Disease Control and Prevention (CDC), The American Academy of Pediatrics, and the Food and Drug Administration (FDA) all have information on their websites detailing vaccine use and the risk of autism spectrum disorder (ASD).

Always ask any questions you may have of your pediatrician or other health care provider, too; they will have the latest updates.

Finished: Vaccines and Autism - Is There A Link?

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  • Pfizer-BioNTech Announce Positive Topline Results of Pivotal COVID-19 Vaccine Study in Adolescents. Clinical Trials. Accessed April 9, 2021 at
  • Frequently Asked Questions about COVID-19 Vaccination. CDC. Acessed April 9, 2021 at
  • US Centers for Disease Control and Prevention (CDC). Thimerosal in Vaccines. Accessed March 19, 2021 at
  • Largest Study Ever Finds No Link Between Measles Vaccine, Autism. Accessed March 4, 2019
  • Measles Cases and Outbreaks. US Centers for Disease Control and Prevention (CDC). Accessed March 21, 2021 at
  • Hviid A, Hansen JV, Frisch M, Melbye M. Measles, Mumps, Rubella Vaccination and Autism: A Nationwide Cohort Study. Ann Intern Med. [Epub ahead of print ] doi: 10.7326/M18-2101. Accessed March 27, 2020.
  • Anti-Vaccine Movement Affecting Kids With Autism (JAMA Pediatrics). March 26, 2018. Accessed March 27, 2020.
  • Autism Prevalence on the Rise: 1 in 68 Children Diagnosed With Autism Spectrum Disorder. American Academy of Pediatrics (AAP). Accessed March 27, 2020.
  • The U.S. Centers for Disease Control and Prevention (CDC). Vaccines Do Not Cause Autism. Accessed March 21, 2021 at
  • Wakefield, AJ, et al. RETRACTED: Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Accessed March 21, 2021 at

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.