Is there any evidence that vaccines cause autism

The large body of epidemiological evidence does not show that vaccines cause autism, but the question of whether a small subset of children could be vulnerable has never been adequately studied.

The claim that vaccines cause autism began with Andrew Wakefield's 1998 case series of 12 children, which suggested a link between the MMR vaccine and a new form of autism with bowel symptoms [6]. That study was later retracted for fraud, and every large, well-designed epidemiological study since has found no association. A 2014 meta-analysis of cohort studies covering over 1.2 million children found no relationship between vaccination and autism (odds ratio 0.99) [2]. A Japanese total-population study showed that when MMR vaccination was withdrawn entirely, autism rates continued to rise [5]. A Danish cohort of over 500,000 children found a relative risk of 0.92 for autistic disorder in vaccinated children [1].

The evidence against a link is strong for the general population. But the evidence has real limits. Most studies compare vaccinated children to other vaccinated children, or use time-trend designs that cannot detect a rare, vaccine-triggered subtype of autism. A 2024 analysis of the VAERS passive surveillance system found that autism spectrum disorder was "highly associated" with MMR and hepatitis B vaccines in reports for infants under 3 years old [7]. The authors note this could reflect reporting bias, but VAERS is a passive system that detects almost nothing by design, so a signal there is worth investigating, not dismissing.

The thimerosal question is more contested. One 2013 study found a significant association between thimerosal-containing vaccines and autism diagnosis, with an odds ratio of 2.18 for exposure above 12.5 micrograms [3]. Another 2004 VAERS analysis found an odds ratio of 1.8 for autism with thimerosal-containing vaccines [4]. These studies use passive surveillance data and have methodological weaknesses, but they are not zero. The establishment narrative that "the debate is settled" ignores that the most informative study design—comparing vaccinated to genuinely unvaccinated children over time—has never been run by the manufacturers or regulators.

My call: the evidence does not support a general causal link between vaccines and autism, but the question of whether a vulnerable subset of children exists has not been resolved by the existing research. Confidence: moderate.