A COMPREHENSIVE evidence review conducted by the World Health Organization (WHO) has reaffirmed that vaccines, including those containing thiomersal, are not associated with autism spectrum disorder (ASD).
Robust Methodology
The review, spanning studies published between 2010–2025, aimed to address public concerns about vaccine safety and provide clarity on the relationship between vaccines and neurodevelopmental disorders (NDD). Experts analysed 36 peer-reviewed studies, including 31 primary research articles and five meta-analyses, alongside 21 narrative reviews. The review examined the relationship between thiomersal-containing vaccines and ASD, as well as the broader association between vaccines and ASD. Studies were assessed for methodological quality, strength of evidence (SoE), and risk of bias (RoB).
Thiomersal and General Vaccines Show No Causal Link to Autism
For thiomersal-containing vaccines, nine studies reported no association with ASD or NDDs, while nine studies suggested a positive association. However, the studies reporting an association were found to have very low SoE and high RoB due to methodological flaws, such as reliance on administrative coding and passive reporting. Two meta-analyses, synthesising data from 26 primary studies, concluded there was no credible evidence linking thiomersal-containing vaccines to ASD.
Regarding vaccines in general, 17 studies and four meta-analyses found no association between vaccination and ASD. This included large-scale cohort studies involving nearly 800,000 children from multiple countries. Two studies reported a positive association, but both had very low SoE and high RoB, limiting their reliability.
Evidence-Based Communication and Global Action
The WHO review highlights that the most robust scientific evidence consistently rejects a causal link between vaccines and ASD. The findings align with previous reviews and reinforce the safety of vaccines, including those containing thiomersal. The report emphasises the importance of transparent communication and evidence-based policymaking to counter misinformation and vaccine hesitancy. Vaccines remain one of the most effective public health interventions, preventing millions of deaths annually.
The WHO urges continued research into vaccine safety and calls for global efforts to ensure equitable access to safe vaccines, particularly in low- and middle-income countries.
Reference
World Health Organization (WHO). WHO expert group’s new analysis reaffirms there is no link between vaccines and autism. 2025. Available at : https://www.who.int/news/item/11-12-2025-who-expert-group-s-new-analysis-reaffirms-there-is-no-link-between-vaccines-and-autism. Last accessed: 15 December 2025.
