Rebecca Bell, MD, MPH, is a pediatric critical care physician at The University of Vermont Children’s Hospital.
One of the most common questions parents have about vaccines is whether or not they “cause autism.” While there is no scientific evidence of a link between vaccines and autism, parents continue to see misinformation on social media and hear comments from celebrities and politicians that suggest a link may exist. Recent media coverage has focused on Andrew Wakefield, a former physician from the UK, who has released a film claiming a link. This conflicting information is confusing to parents who are looking for answers.
What do we know about vaccines and Autism Spectrum Disorder (ASD)?
A lot, actually. The question has been studied extensively over many years, across multiple continents and has included more than a million children. This large body of evidence shows no link between vaccines and ASD. Medical and scientific organizations have stated unequivocally that research shows vaccines do not lead to ASDs, including the Centers for Disease Control, the National Institutes of Health, the American Academy of Pediatrics, the World Health Organization and the Institute of Medicine, among others.
Let’s take a closer look at what the evidence says about some common questions parents have.
What did Andrew Wakefield’s study show?
Wakefield’s now retracted 1998 paper suggested a possible link between the MMR vaccine, bowel disease, and autism. He and his co-authors described 12 children of whom 8 had regressive behaviors that their parents say started after the MMR vaccine. Despite the small number of patients, the reliance on parents’ reports and the lack of controls, the paper set off a storm of public concern and MMR vaccination dropped significantly in the UK and elsewhere.
So Wakefield put forward a hypothesis. Was it adequately tested?
Once a hypothesis is generated from a small case series such as the Wakefield paper, the next step is to test it over large populations and in a rigorous manner to see if it holds up. None of these rigorous studies showed a link between MMR vaccine and ASD. Here are a few examples of studies with links to the original papers:
- Hundreds of children with an autism diagnosis born in the UK from 1979-1998 were studied. There was no change in the trend of autism diagnoses when the MMR vaccine was introduced in 1988. There was no difference in age at diagnosis between those vaccinated and those never vaccinated. Timing of developmental regression was not associated with the vaccine. A re-analysis evaluating a longer time period after the vaccine was given also showed no link.
- Records from more than 500,000 Danish children were evaluated. There was no increased risk of autism or other ASDs in those vaccinated with MMR compared with those not vaccinated. There was no association with timing of vaccine and diagnosis of autistic disorder.
- A UK case-control study matched over 1,200 children with ASD with over 4,000 controls and found that the MMR vaccine did not increase the odds of diagnosis of ASD.
- A study in California compared trends in ASD diagnosis and MMR vaccine in children between 1980-1994 and found that while the number of ASD cases in the population rose dramatically, the rate of MMR vaccination remained the same. A similar study in the UK had the same findings.
- A population of over 95,000 US children was analyzed in a 2015 paper and no link was found between MMR vaccine and ASD even among children with an older sibling with ASD.
Meanwhile, as more and more studies were showing no link between the MMR vaccine and ASD, the UK’s General Medical Council (GMC) was investigating Wakefield and his research. The Council discovered that Wakefield had not disclosed that he was paid a substantial amount of money by a lawyer representing parents who believed their children had been harmed by the MMR vaccine and that he had been dishonest about how patients were recruited for the study. He was also found guilty of performing unnecessary invasive procedures on children. In 2010, the GMC stripped Wakefield of his medical license and he is no longer allowed to practice medicine. In addition, further examination of the study has shown widespread and significant falsification of data. Wakefield had also applied for a patent on a single-dose measles vaccine prior to the study and did not disclose this and other conflicts of interest.
In summary, Wakefield’s claim that MMR could be linked to autism based on his small, poorly-controlled observational paper has been refuted by many large well-controlled studies. In addition, he has been found guilty of multiple ethics violations in connection with the study and has lost his medical license.
OK, so the MMR vaccine is not linked to ASDs. But what about vaccine ingredients?
This, too, has been studied. Up until 1999, some vaccines had an ethylmercury-containing preservative called thimerosal. Studies have shown that thimerosal has no link to autism. Thimerosal is no longer contained in any childhood vaccines other than some multi-dose influenza preparations. If you have questions about other vaccine ingredients, you can read about them here.
Maybe it’s the combination of too many vaccines at once?
As scientists have developed more vaccines to prevent disease, some parents worry that their infants are receiving too many vaccines at once. What they may not know is that immunizations today contain fewer antigens (proteins and sugars that stimulate antibody production) than previously. So even though children receive more vaccines than their parents or grandparents did as children, they are exposed to fewer total antigens. In addition, studies have shown that increasing the number of vaccine antigens does not increase the risk of ASD.
So, I understand the science shows no link to autism, but what’s the harm in not vaccinating my child just in case?
Delaying or skipping immunizations puts children at risk for serious vaccine-preventable illnesses. As pediatricians, it’s our job to protect children from harm. Vaccines are one of the best tools we have to keep children safe.
We don’t have all the answers about autism but we do have evidence that ASDs are related to abnormal brain development during early fetal growth. Scientists have also identified a number of genes associated with autism. For more information on autism research, visit the Autism Science Foundation. For families looking to connect with others in the ASD community or to participate in research, check out the Interactive Autism Network.
Rebecca Bell, MD, MPH, is a pediatric critical care physician at The University of Vermont Children’s Hospital. She is also an assistant professor at the University of Vermont College of Medicine.