Vaccines and Autism: A Clinical Perspective

You may have heard people say that vaccines cause autism. More than 20 rigorous, high-quality studies have found no evidence to support this claim. Yet, it persists, and that can weigh on families trying to make the best decisions about their children’s health. We asked the clinical experts at the Child Mind Institute’s Autism Center to help us understand the origins of the claim, why it persists, and where the current research stands on potential causes of autism

Autism, or autism spectrum disorder (ASD), is a neurodevelopmental disorder, meaning it impacts the development of the brain. Autism is characterized by impairment in social communication skills — a technical way of saying that it affects the way a child engages in conversation, makes friends, and reads social cues. Kids on the autism spectrum also exhibit restricted and/or repetitive behaviors and interests, often called RRBs for short. These can include repetitive movements and use of objects — hand flapping, lining up toy cars, or sorting crayons by color. RRBs can also include strong special interests in very specific topics or things, like sports, transit systems, numbers, anime, or water.

Research suggests that autism may be present in a child before they are born, although it does not fully emerge until the toddler stage at the earliest. And people can be diagnosed with autism at any age. Perhaps their symptoms or autistic traits were harder to see when they were younger, they didn’t meet all the diagnostic criteria yet, or it was overlooked entirely. People with autism have a wide range of social skills and behaviors — that’s why it’s called a spectrum.

Cynthia Martin, PsyD, the senior director of the Autism Center at the Child Mind Institute, says that individual presentations of autism — i.e., how individual autistic people behave and engage with the world — are so diverse that it might actually be more accurate to say “autisms” rather than putting everyone in one big category.

To be diagnosed with autism, a child’s challenges with social communication skills and RRBs must impact their daily functioning in ways that require some degree of support. For some kids, support means accommodations in school or seeing a therapist a few times a week; for others, it means round-the-clock help with basic personal care.

No. After the publication of more than 20 research studies directly examining the claim, there remains no scientifically acceptable evidence that vaccines cause autism. But it’s helpful to understand where the idea came from and why people have singled out the MMR vaccine in particular.

The MMR vaccine is a combination vaccine that provides immunity against three exceptionally dangerous and life-threatening diseases: measles, mumps, and rubella. It was developed in 1971.

Before a vaccine was available, almost all children contracted measles before the age of 15. The disease killed 1–2 children out of 1,000, and there is no specific treatment for it. Meanwhile, exposure to rubella during pregnancy can cause miscarriages, stillbirths, and serious birth defects. Mumps is less deadly but can cause swelling around the brain and lifelong complications, such as deafness.

The MMR vaccine protects individuals from contracting these diseases and in doing so, protects the larger community. Take measles, which has an astonishing 90% infection rate. Even a few people without immunity can cause a population outbreak. (Two doses of the MMR vaccine are 97% effective in preventing measles; one dose is about 93% effective.) Low immunization rates — driven in part by parents choosing not to vaccinate their children — led to a 20% increase in measles cases worldwide between 2022 and 2023.

In 1998, then medical doctor Andrew Wakefield published an article in the Lancet, a respected medical journal. In it, he claimed evidence that the MMR vaccine could cause symptoms of autism in children. But the paper was seriously flawed. Further investigations found that Wakefield had manipulated and even falsified data in addition to other serious ethical violations — all of which were later acknowledged by the Lancet.

The Wakefield paper was based on case reports of 12 children. This is important because 1) valid studies need to involve a lot more participants to demonstrate significance and even more to appropriately represent the larger population; and 2) a case report isn’t actually a study. Case reports provide detailed medical histories for individual patients. They can be very useful for collecting data — or for pointing to an issue worthy of further study — but they’re not built to support claims on their own.

In 2010, the independent British General Medical Council (GMC) found Wakefield guilty on 30 charges of professional misconduct. The council was particularly outraged by his “callous disregard” for the report’s child participants and his misrepresentation of their symptoms. They also cited him for various ethical violations, noting that his research was paid for in part by lawyers seeking to sue vaccine makers. The Lancet retracted the article, and Wakefield lost his medical license.

Meanwhile, other researchers tested Wakefield’s claim. Dozens of reports were published, including two consecutive studies involving every child born in Denmark over a 30-year period. None could find any link between the MMR vaccine and autism.

Wakefield and his report received a lot of media attention, creating a link between vaccines and autism in public thought. The claim was so ubiquitous that, regardless of your opinion, it was likely you had heard it. And for some, the link seemed to make sense because of coincidence. Signs of autism typically begin to appear between the ages of 0 and 2 because doctors, caregivers, and parents are tracking a child’s social-communication milestones — making eye contact, using hand signals, responding to their name — in real time. This is also around the time it’s recommended that kids receive the first dose of the MMR vaccine.

“If you see things happening to your child right next to each other, it’s a normal parenting instinct to be like, ‘Oh, there should be some link,’” says Dr. Martin, who is also a parent.

Once the association between the MMR vaccine and symptoms of autism had been made, people understandably thought they saw “evidence” that one had caused the other — which can be a powerful personal motivator, even when all scientific evidence shows that the two events are unrelated. But what parents saw was correlational (when two things happen at the same time) not causal (when one thing causes another).

There is no reason for concern about ingredients in vaccines — and scientists aren’t saying that lightly. Vaccine opponents often single out a preservative containing mercury called thimerosal as a cause for alarm. The Federal Food and Drug Administration (FDA) asked companies to remove thimerosal from vaccines beginning in 1999 as a precaution, and since then, dozens of studies have shown it to be safe. But in 2000, several parent groups raised the claim that thimerosal caused autism.

Researchers embarked on dozens of studies and examined decades worth of data across multiple countries to test the claim. They could not find any link between vaccines, thimerosal, or mercury and autism. Mercury sounds terrifying, but to be clear, thimerosal contains a small and safe amount of the same variety found in fish — and about as much of it as you would find in a three-ounce can of tuna.

More importantly, the MMR vaccine never contained thimerosal to begin with.

The honest answer is we don’t fully know right now — but here’s a little background about what we’ve learned about autism and a snapshot of where the research currently stands.

Autism was first identified in the 1940s, but it didn’t become a formal diagnosis until it appeared in the Diagnostic and Statistical Manual of Mental Disorders, the DSM-3, in 1980.

The definition was revised to include more criteria for diagnosis in 1987, and it has further expanded in subsequent versions of the manual. The most current version, the DSM-5, now includes under autism some disorders that had been previously categorized separately. For example, Asperger’s Disorder was once a separate diagnosis but is now consolidated into autism spectrum disorder.     

In 2000, 1 in 150 children in the United States were diagnosed with autism. In 2025, the CDC reported it was 1 in 31. 

When clinicians see the figure from the CDC, it tells them that more children are being diagnosed with autism by a doctor or being classified as having autism on their school IEP because of the way the statistics are calculated. In the past, lots of people who had autism weren’t diagnosed, so they weren’t captured in the statistics. And parents and clinicians are getting better at recognizing autism at different ages and getting kids diagnosed so they can get the help they need.

As our understanding of autism rapidly evolves, so does genetic research into its causes. “When I was a medical student, there were just a few genes known to be involved with autism,” says Adriana Di Martino, MD, the founding and research director of the Autism Center at the Child Mind Institute. Today, researchers have identified over 100 — evidence that there are multiple causes, and likely pathways, involved in how autism develops.

Autism is thought to arise from a complex interplay of factors that influence early brain development. These include genetic, prenatal, and, to some degree, environmental factors.

Genetic contributions include heritability, rare mutations, and common polygenic variations (meaning there are multiple genes that contribute to autism susceptibility). Various prenatal and environmental factors that have been implicated in an increased likelihood of autism include advanced parental age, particularly older fathers; maternal infections; toxin exposures; metabolic conditions during pregnancy; and birth complications.

Clinicians emphasize the importance of autism awareness, education, and early intervention. Because the earlier a child is diagnosed, the earlier they can start receiving support.

“We need to get kids diagnosed as early as autism symptoms become detectable,” Dr. Martin says. “Then we need to have individualized and well-tailored interventions that are meaningful and make sense for that child. And support them in having the best quality of life possible.”