Written by Dr. Amanda Kelly
A recent Healthier Colorado survey conducted in 2025 by Magellan Strategies found that 31% of Coloradans believe vaccines may cause autism in children. This comes at a time of significant national changes in vaccine policy: the Food and Drug Administration (FDA), Centers for Disease Control (CDC) and Advisory Committee on Immunization Practices (ACIP) have all made headlines recently for updated vaccine recommendations, with the US Department of Health and Human Services adopting the removal of thimerosal, a mercury based preservative, from all flu vaccines.
These changes have sparked renewed public discussion and, in some cases, confusion regarding vaccines and autism. Uptake for school-required immunizations is declining somewhat across Colorado, with personal choice exemptions on the rise. Amid this shifting landscape, oversimplified narratives about “vaccines” and “autism” are spreading. These are not single, uniform concepts. They each involve multiple variables and complex contexts. To support informed decision-making, it is critical to provide clear, balanced, and evidence-based information that addresses myths directly while respecting concerns.
One of the most enduring sources of confusion stems from a famously retracted paper published in 1998, which implied a link between the MMR vaccine and autism due to its multiple-dose nature. Decades of follow-up studies have found no validity to this claim. Similarly, Thimerosal, the mercury based preservative found in large batch (versus single dose) flu vaccines was once linked to autism. That claim has been refuted repeatedly, and thimerosal was removed from all routine childhood vaccines (e.g., MMR, meningitis) in the U.S. by 2001, which was precautionary versus due to proven harm. The removal of any mercury and continuous diligent research into vaccine safety is positive and will be reassuring to some, however the issue is a lack of clear and transparent information leading to public confusion.
Autism itself is highly complex and often misunderstood. It is a developmental difference that exists on a broad spectrum, with diagnoses typically classified as levels 1, 2, or 3 based on support needs. Autism diagnoses may include co-occurring conditions and can occur with or without intellectual disability. It is highly individualized, with no single clear “cause”.
Research shows that a strong genetic component underlies most cases: inherited genetics and spontaneous gene mutations combined are thought to account for somewhere between 70–90% of autism cases. Twin studies, family history data, and the identification of hundreds of autism-associated genes support this. Environmental factors may also play a role, but the picture is nuanced, encompassing both prenatal factors (e.g., advanced maternal/paternal age, maternal infections, smoking, toxin exposure) and postnatal factors (e.g., recurring infections in early childhood) (Lebeña et al., 2024). It is also possible that environmental variables influence how certain genes express, rather than acting as direct causal agents.
In short, no vaccine ingredient, alone or in combination, has been shown to “cause autism.” It’s just not that simple and insinuating otherwise is harmful. Parents and caregivers already hold so many unknowns and guilt when it comes to their children’s health and wellbeing — this is something that deserves clear information and careful consideration. Confusion about vaccines and autism can also lead to lower vaccination rates, putting communities at risk for preventable infections and diseases. By sharing the facts in a balanced way and helping educate about what autism is and is not, we can promote greater understanding and acceptance of autism as a natural part of human diversity.
