Vaccines, thiomersal and autism spectrum disorder: evidence review 2010-2025

Overview

This systematic review provides a current assessment of peer-reviewed studies published between 2010 and August 2025 investigating potential associations between vaccines and autism spectrum disorder (ASD), with particular focus on the organomercury vaccine component thiomersal, and also considers studies reporting other neurodevelopmental disorders (NDD). It updates previous WHO reviews by assessing the methodological quality, strength of evidence and risk of bias of the available literature. The review finds that the most methodologically rigorous primary studies do not support a causal association between vaccines, including thiomersal-containing vaccines, and ASD. Studies reporting positive associations had very low strength of evidence and high risk of bias, while none of the included meta-analyses supported a causal relationship. Overall, the evidence continues to support the safety of current vaccines with respect to ASD and other NDD. The review aims to provide clinicians, policy-makers and public health professionals with reliable and balanced evidence to inform decision-making, strengthen vaccine confidence and contextualize ongoing scientific and public dialogue.