A Tale of Three Theories: Vaccines & Autism

Published July 17th, 2020 by Dr. Miriam Opara, PharmD
Fact Checked by
Chris Riley

The controversy surrounding vaccines and autism has existed for two decades and continues to this day, with 10% of American adults reporting they believe vaccines cause autism in a recent Gallup poll. 

This view persists despite the increased scrutiny that vaccines have received and numerous studies that have failed to show an association between vaccine exposure and autism. 

What is certain – is the decreased vaccination rates and withholding of vaccines has contributed to major outbreaks in recent years, such as Measles outbreaks on both the East and West Coast of the U.S. in 2019. 

So…why does the vaccine-autism controversy endure? 

Theory 1: The Measles, Mumps, and Rubella (MMR) Vaccine is Linked to Autism

The MMR controversy began in the late 1990s with the publication of a small study (that included 12 children) by Andrew Wakefield et al. in which he claimed a link between the administration of the MMR vaccine and the development of autism. 

Wakefield based his claim on the observation that eight out of twelve children in his study were diagnosed with autism within 4 weeks of receiving the MMR vaccine. He also recommended to stop providing the combo MMR vaccine in favor of single separate vaccines. Interestingly, Wakefield had also filed for a patent for a single measles vaccine before the publication of his study, seriously calling his motives into question. 

Further, in order to determine whether MMR causes autism, a study needs to look at how many children develop autism in both vaccinated and unvaccinated children; this was not done in Wakefield’s study. Moreover, Wakefield failed to disclose that he received research money from a law firm hoping to sue vaccine manufacturers on behalf of parents of children with autism. 

Ultimately, the study was fully retracted in 2010 because of false information, misrepresentation of data, ethical violations, and conflicts of interest. Wakefield was discredited, and his medical license revoked in the United Kingdom. 

Even though the study was discredited, the fear that vaccines are associated with autism began to spread, and people (including some celebrities) began to question whether there was a link. Fear led to significant drops in vaccination rates, thousands of cases of measles, and tragic deaths that could have been prevented. 

Theory 2: Thimerosal-Containing Vaccines Cause Autism

Once the MMR vaccine link controversy slowed, thimerosal (an antibacterial compound that contains 50% ethyl mercury) was the next to be targeted.

Thimerosal has been used in vaccine multidose containers for over 50 years. In 1999, the FDA found that children might be receiving as much as 187.5 micrograms within the first six months of life. 

Although there was no evidence of harmful ethyl mercury quantities contained in vaccines, The American Academy of Pediatrics recommended the immediate removal of mercury from all vaccines given to young infants. 

The timing of these recommendations with the Wakefield study further fueled public concern over the link between autism and vaccinations. However, multiple studies have failed to show an association between thimerosal and autism:

  • A meta-analysis (looked at ten studies) involving more than 1.2 million children determined that vaccines are not associated with autism. The analysis showed there was no relationship between vaccination and autism or a link between autism and thimerosal or mercury.
  • Twenty epidemiologic studies comparing the prevalence of MMR vaccine and the diagnosis of autism concluded that thimerosal and MMR vaccine are not causes of autism. 
  • A nationwide cohort study in Denmark evaluated whether the MMR vaccine increases the risk for autism in over 600,000 children. The study strongly supported MMR vaccination and found no increased risk of autism and nothing to support autism being triggered by the MMR vaccine. 
  • Another study analyzed health records of over 95,000 children in the U.S., with 2,000 considered at risk for autism because they had an older sibling already diagnosed with autism. The study confirmed that the MMR vaccine did not increase the risk of autism. 
  • This study looked at 477,000 children in Demark and compared children who were vaccinated with a thimerosal-containing vaccine and those who received a thimerosal-free formulation of the same vaccine. There was no causal relationship or increased risk of thimerosal-containing vaccines and the development of autism. 

Despite the lack of an association, today, thimerosal is no longer included in most childhood vaccines. 

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Theory 3: The Number of Vaccines Given at a Young Age Increases Risk of Autism 

After thimerosal was removed from childhood vaccines, the rate of autism did not decrease…it increased. Critics then offered the number of vaccines recommended per the childhood immunization schedule and vaccine exposure as the next theory for autism. The number of vaccines recommended in early childhood has increased significantly since the 1980s. 

Even with the increased number of vaccines recommended, no evidence has demonstrated an association between the number of vaccines given at a young age and autism. 

  • A study conducted by the CDC looked at different types of dead viruses (antigens) from vaccines. The results showed that exposure to antigens contained in vaccines did not change the risk of being diagnosed with autism.  
  • Another study looked at vaccine antigen exposure in children ages 24-47 months with infections (like pneumonia, croup, ear infections, pharyngitis) compared with children who did not get infections. A total of 994 children were involved in the study, and there was no correlation between exposure to antigens through vaccines and the risk of developing infections. 

Bottom Line: 

Vaccines have proved themselves to be a safe and effective tool to fight preventable diseases. 

Since the Wakefield study, there have been more than 25 studies that have shown no causal association between vaccines and autism in over 14,00,000 children. There is also no evidence to support thimerosal or vaccine exposure causing autism either. 

Children should be vaccinated per the yearly CDC immunization schedule unless otherwise recommended by your primary care provider. 


Published July 17th, 2020 by Dr. Miriam Opara, PharmD
Fact Checked by
Chris Riley

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