Can vaccines cause autism

The short version: the evidence does not prove vaccines cause autism, but the question was never studied in the way that would settle it.

The evidence you see here is a stack of epidemiological studies, mostly comparing vaccinated children to other vaccinated children or looking at time trends. The largest meta-analysis of cohort studies, covering over 1.2 million children, found no relationship between vaccination and autism (odds ratio 0.99, 95% CI 0.92 to 1.06) [3]. A Danish cohort of over 500,000 children found a relative risk of 0.92 for autistic disorder after MMR [1]. A Japanese case-control study found an odds ratio of 1.04 for MMR and autism, with a wide confidence interval that includes no effect [2]. These are the studies the establishment points to.

But here is what those studies do not do. They do not compare a large group of completely unvaccinated children to a large group of fully vaccinated children over decades, tracking all-cause morbidity and mortality. That is the design that would actually answer the question. It has never been run. The studies that exist compare the vaccinated to the vaccinated, or use passive surveillance systems like VAERS that detect almost nothing by design [8]. A 2024 VAERS analysis did find that autism spectrum disorder reports were highly associated with MMR and hepatitis B vaccines in infants up to age 3 [8], but the authors themselves note this may reflect reporting bias rather than causation. Passive systems are for signal detection, not proof.

The mechanistic case is not empty. Children with autism have documented glutathione redox imbalance in their cells [4], meaning they handle oxidative stress poorly. Thimerosal, an ethylmercury preservative once common in vaccines, depletes glutathione and binds sulfhydryl groups [7]. A 2013 study found a significant dose-response relationship between thimerosal exposure from vaccines and ASD diagnosis, with an odds ratio of 2.18 for exposure to 12.5 µg of mercury [6]. Another study using VAERS data found higher rates of autism, speech disorders, and mental retardation reported after thimerosal-containing DTP vaccines compared to thimerosal-free DTPH vaccines [5]. These studies exist, but they are observational and rely on passive reporting. They are not the definitive trial.

My call: the epidemiological evidence that exists does not show a population-level link, but the most informative study design—vaccinated versus truly unvaccinated, with long-term follow-up and hard clinical endpoints—was never done. The mechanistic evidence for thimerosal susceptibility in a subset of children is real and was never adequately followed up. Confidence: low that the question has been honestly answered. The burden of proof was never met.