WHO publishes updated evidence review on vaccines, thiomersal and autism spectrum disorder

A new World Health Organization systematic review finds that the strongest available evidence does not support a causal association between vaccines, including thiomersal-containing vaccines, and autism spectrum disorder.

The World Health Organization (WHO) has published an updated systematic review examining the evidence on potential associations between vaccines, thiomersal and autism spectrum disorder (ASD).

Published on 3 September 2026, Vaccines, thiomersal and autism spectrum disorder: evidence review 2010–2025 assesses peer-reviewed research published between January 2010 and August 2025. The review updates previous WHO assessments and considers the methodological quality, strength of evidence and risk of bias of the available research.

What did the review find?

The review included 31 primary research studies: 16 examining thiomersal-containing vaccines and ASD and 15 examining vaccines and ASD more broadly. It also considered five meta-analyses.

The review found that the most methodologically rigorous primary studies did not support a causal association between vaccines, including thiomersal-containing vaccines, and ASD. All five meta-analyses included in the review also found no evidence supporting an association.

Studies that reported a potential association were assessed as having very low strength of evidence and a high risk of bias due to significant methodological limitations.

Overall, WHO concluded that the available evidence continues to support the safety of current vaccines with respect to ASD and other neurodevelopmental disorders.

The review provides clinicians, policymakers and public health professionals with an up-to-date assessment of the evidence to support informed decision-making and vaccine communication.

Read the full WHO review:
Vaccines, thiomersal and autism spectrum disorder: evidence review 2010–2025