WHO Safety Panel Updates Evidence Review, Confirms Vaccines Do Not Cause Autism

The World Health Organization’s Global Advisory Committee on Vaccine Safety (GACVS) has again concluded that vaccines do not cause autism, following an updated, methodologically rigorous review of the scientific literature. The committee’s latest assessment, completed on November 27, 2025, re-examined the question using 2 new systematic reviews covering research published from 2010 through mid-2025.

GACVS bases its determinations on established criteria for causality, with particular emphasis on study design and risk of bias. "We place the greatest weight on high-quality, well-designed studies with low risk of bias, and very little weight on studies with significant methodological flaws,” the committee wrote. Systematic reviews, which evaluate the quality of all available studies and synthesize results, form the foundation of this process.

Review of Thimerosal and Vaccines in General

The first new review updated earlier WHO analyses published in 2012 and included 31 primary studies and 5 meta-analyses from 11 countries. The majority of the methodologically strongest studies, including all meta-analyses, found no association between autism spectrum disorder (ASD) and either thiomersal-containing vaccines or childhood vaccines more broadly.

“Although a small number of studies suggested a potential link, these studies had major methodological limitations and provided very low-quality evidence that cannot support causality,” the GACVS noted. The committee also emphasized that many of the studies suggesting harm originated from a single research group and consistently exhibited high risk of bias.

Review of Aluminium-Adjuvanted Vaccines

The second systematic review evaluated whether aluminium-containing vaccines pose long-term health risks, including neurodevelopmental outcomes. High-quality evidence from randomized trials and large cohort studies found no association between aluminium adjuvants and chronic or systemic disease.

Two ecological analyses had reported correlations between cumulative aluminium exposure and ASD prevalence, but GACVS emphasized that such study designs "are not not suited to determining causality, and each was judged at critical risk of bias.”

As part of its assessment, GACVS also considered a nationwide Danish cohort study published after the review period. This analysis of nationwide registry data for more than 1.2 million children born between 1997 and 2018 found no link between early-life exposure to aluminium-adsorbed vaccines and ASD—or any of 50 chronic childhood conditions examined.

GACVS reaffirmed the conclusions of its prior reviews, first established in 2002 and updated in 2004 and 2012: “The totality of high-quality scientific evidence continues to support the safety of vaccines containing thiomersal, aluminium, or both, with no indication of increased risk for autism,” the committee stated.

The committee highlighted that decades of research from multiple countries continue to support the strong safety profile of vaccines used in pregnancy and childhood.