Does vaccination increase the likelihood of autism?

One hypothesis is that vaccination in general, MMR (measles, mumps, rubella) virus live vaccine, and vaccines that contain mercury cause autism. Actress Jenny McCarthy is one of the most outspoken proponents of the autism-vaccine hypothesis. She has appeared on numerous TV shows, radio shows and other media outlets where she has claimed that there is definitely a link between vaccines and autism.

Former presidential candidate John McCain stated, “It’s indisputable that autism is on the rise amongst children, the question is what’s causing it… There’s strong evidence that indicates that it’s got to do with a preservative in vaccines.”

President Obama stated, “We’ve seen just a skyrocketing autism rate. Some people are suspicious that it’s connected to the vaccines — this person included.”

What Science Says About Vaccines and Autism

Solt and Bornstein reviewed studies that investigated the autism-vaccine hypothesis. The researchers concluded that:

Studies that investigated this theory [hypothesis] did not find an association between vaccine administration and between digestive system symptoms and autism. According to a second hypothesis, an organomercury compound (Thimerosal), used as a preservative in vaccines that do not include live viruses, is a cause of autism. Like the former, this hypothesis has been well researched, and refuted. Some studies have in fact found an increase in autism diagnosis among children who were vaccinated after Thimerosal was removed from the vaccine preparation. Recent studies have refuted the theory that the consecutive administration of vaccines weakens the young immune system in children, and leads to an autoimmune process that causes autism.

Exposure to thimerosal, a mercury-containing preservative found in vaccines and immunoglobulin preparations, has been hypothesized to be associated with increased risk of autism spectrum disorder (ASD). A study conducted by Price and colleagues (2010) examined relationships between prenatal and infant ethylmercury exposure from thimerosal-containing vaccines or immunoglobulin preparations, and ASD and 2 ASD subcategories (autistic disorder and autism spectrum disorder with regression). The researchers concluded that prenatal and early-life exposure to ethylmercury from thimerosal-containing vaccines and immunoglobulin preparations was not related to increased risk of ASDs.

Lilienfeld and colleagues (2010, p.198) point out:

[T]here’s no solid evidence for any link between autism and vaccinations — including either injections containing thimerosal or injections for MMR (measles, mumps, and rubella; Institute of Medicine, 2004; Offit, 2008)

[S]everal large American, European, and Japanese studies revealed that even as the rates of vaccinations stayed the same or went down, the rates of diagnosed autism increased (Herbert, Sharp, & Gaudiano, 2002; Honda, Shimizu, & Rutter, 2005). Even after the government removed thimerosal from vaccines in 2001, the rates of autism in California continued to climb rapidly until 2007 (Schechter & Grether, 2008).

Vividness Effect

Scientific evidence does not support the autism-vaccine link. However, compelling personal testimonials often dissuade people from accepting the scientific evidence. The vividness of personal testimony often trumps evidence of higher reliability. This problem in belief formation occurs due to what cognitive psychologists call the vividness effect. Society is replete with examples of the vividness effect. To further illustrate this point consider the following scenario. You are deciding whether you should try a dietary supplement that is purported to decrease appetite. After reading the scientific research on the product you conclude that the supplement does not decrease appetite. The next day you mention the supplement to your friend, who suggests the supplement worked great for her. Should this anecdote persuade you to purchase the supplement, even though scientific data suggests otherwise? There is a good chance that the friend’s testimony would outweigh the scientific evidence. The vividness effect is evident with the acceptance of the autism-vaccine link. Most people don’t read scientific journals and the majority of media reports aren’t concerned with what science says, but with what makes good headlines.

The public’s misunderstandings of the autism-vaccine link may be very dangerous. In 2008, the New York Times reported increases in measles in the U.S., Italy, Switzerland, Austria, and Italy; these are all areas where many parents have declined vaccinations for their children.


Lilienfeld, S. Lynn, S. Ruscio, J. Beyerstein, B. (2010). 50 Great Myths of Popular Psychology: Shattering Widespread Misconceptions about Human Behavior. Malden , MA: Wiley-Blackwell.

Price, CS et. al. (2010). Prenatal and infant exposure to thimerosal from vaccines and immunoglobulins and risk of autism. Pediatrics Oct;126(4):656-64.

Solt, I. Bornstein, J. (2010). Childhood vaccines and autism — much ado about nothing? Harefuah Apr;149(4):251-5, 260.

Stanovich, K. (2007). How To Think Straight About Psychology. 8th edition. Boston, MA: Pearson.