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The McCullough Foundation Report: Determinants of Autism Spectrum Disorder (2025) presents an extensive review of 136 studies exploring possible causes of Autism Spectrum Disorder (ASD). The authors write that ASD “is now estimated to affect more than 1 in 31 children in the United States” and results from a convergence of “genetic liability, immune dysregulation, perinatal stressors, and environmental toxicants.”
Among the potential determinants identified, the report lists:
“Older parents (>35 years mother, >40 years father), premature delivery before 37 weeks, common genetic variants, siblings with autism, maternal immune activation, in-utero drug exposure, environmental toxicants, gut-brain axis alterations and combination routine childhood vaccination.”
Vaccine-Related Findings
According to the report’s results section:
“Of 136 studies examining childhood vaccines or their excipients, 29 found neutral risks or no association, while 107 inferred a possible link between immunization or vaccine components and ASD or other neurodevelopmental disorders (NDDs) … 12 studies comparing routinely immunized versus completely unvaccinated children or young adults consistently demonstrated superior overall health outcomes among the unvaccinated, including significantly lower risks of chronic medical problems and neuropsychiatric disorders such as ASD.”
The authors further state that:
“Neutral association papers were undermined by absence of a genuinely unvaccinated control group … and averaged estimates that obscure effects within vulnerable subgroups.”
They describe biologic mechanisms potentially connecting vaccination to neurodevelopmental outcomes:
“Antigen, preservative, and adjuvant (ethyl mercury and aluminum) induced mitochondrial and neuroimmune dysfunction, central nervous system injury, and resultant incipient phenotypic expression of ASD. Clustered vaccine dosing and earlier timing of exposure during critical neurodevelopmental windows appeared to increase the risk of ASD.”
The report notes a parallel between “strong, consistent increases in cumulative vaccine exposure during early childhood and the reported prevalence of autism across successive birth cohorts,” adding that “no study has evaluated the safety of the entire cumulative pediatric vaccine schedule for neurodevelopmental outcomes through age 9 or 18 years.”
Conclusion
Summarizing its findings, the report concludes:
“Combination and early-timed routine childhood vaccination constitutes the most significant modifiable risk factor for ASD, supported by convergent mechanistic, clinical, and epidemiologic findings … Clarifying the risks associated with cumulative vaccine dosing and timing remains an urgent public health priority.”
Source: McCullough Foundation Report — Determinants of Autism Spectrum Disorder, 2025 (Zenodo DOI 10.5281/zenodo.17451259
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