On 27 November 2025, the WHO Global Advisory Committee on Vaccine Safety (GACVS) assessed two new systematic literature reviews, performed using robust methodology, on the potential relationship between vaccines and autism spectrum disorder (ASD)
Upon comprehensive review of the latest evidence published from January 2010 until August 2025, the Committee reaffirmed its previous conclusion based on extensive reviews conducted in 2002[1][2], 2004[3], and 2012[4], that there is no evidence of a causal relationship between vaccines and ASD.
A causal relationship between a vaccine and an event is suspected when several high-quality studies indicate a statistical association between exposure to the vaccine and the outcome of interest. In systematic reviews, databases are searched to ensure comprehensive capture of published studies and the quality of all included studies is evaluated according to well accepted methodologies. When reviewing the evidence to inform causality, the greatest weight is put on the high-quality well-designed studies with low risk of bias and little weight is given to those with methodological flaws and high risk of bias.
The first systematic review examined the relationship between thiomersal-containing vaccines and ASD, as well as the association between vaccines in general and ASD. This review was an update to a previous systematic review conducted in 2012, and encompassed publications in English from January 2010 to August 2025. In total, 31 primary research studies were included:16 specifically on vaccines containing thiomersal and ASD and 15 on vaccines and ASD more broadly. In addition, five meta-analyses (one on thiomersal and ASD, three on vaccines and ASD, and one that examined both) that summarized research also published before 2010 were included.
Twenty of the 31 primary research papers originating from 11 different countries and including studies that were the most methodologically rigorous, as well as all five meta-analyses, found no evidence supporting an association between vaccines, irrespective of thiomersal content, and ASD. The other eleven studies (with nine originating from one single research group in the United States) suggested a potential association; however, these had multiple and significant methodological issues, and all had very low strength of evidence and a high risk of bias. Taken together, the large body of available high-quality scientific evidence, spanning decades and including data from multiple countries, continues to strongly support the positive safety profile and absence of a causal link with ASD of vaccines used in childhood and pregnancy. Full report of the review will soon be available at https://www.who.int/publications).
The second systematic review focused on human studies assessing potential health risks associated with aluminium-adjuvanted vaccines, covering publications from six literature databases and other literature sources (up to March 2023). High-quality evidence from ten randomized controlled trials and seven large cohort studies found no association between aluminium-adjuvanted vaccines and chronic or systemic diseases. Two studies reported an association between cumulative aluminium exposure from vaccination and ASD prevalence; however, both of these studies were ecological and by design unable to inform causality. These studies also had other methodological limitations and were judged at critical risk of bias, and, hence, their level of evidence was rated as very low.
GACVS also reviewed a recent study on the safety of aluminium-containing vaccines published after the period covered by the above systematic review[5]. This large cohort study used a robust methodology to examine nationwide registry data on children born in Denmark between 1997 and 2018, and found that the incidence of 50 chronic disorders, including ASD and other neurodevelopmental disorders, was not associated with early childhood exposure to aluminium-adsorbed vaccines. In summary, the available quality evidence supports no evidence of an association between the trace amounts of aluminum used in some vaccines and ASD and supports the ongoing use of aluminium-containing vaccines.
After its current review, GACVS reaffirms the conclusions from its previous reviews in 2002[1][2], 2004[3], and 2012[4], that the available high-quality scientific evidence indicates that vaccines, including those with thiomersal or aluminium or both, do not cause autism.
[1] Report of Global Advisory Committee on Vaccine Safety, World Health Organization. 2002 (accessed 12 November 2025)
[2] MMR and autism, World Health Organization. 2003 (accessed 12 November 2025)
[3] Weekly epidemiological record, World Health Organization. 2005 (accessed 12 November 2025)
[4] Weekly epidemiological record, World Health Organization. 2012 (accessed 12 November 2025)
[5] Andersson NW, Bech Svalgaard I, Hoffmann SS, Hviid A. Aluminum-Adsorbed Vaccines and Chronic Diseases in Childhood: A Nationwide Cohort Study. Ann Intern Med. 2025; 178:1369-1377. doi: 10.7326/ANNALS-25-00997.