Link between vaccines and autism: A global vaccine-safety committee convened by the World Health Organization has again concluded there is no evidence that vaccines cause autism spectrum disorders, reinforcing the agency’s long-standing position that childhood immunisations are not linked to autism.
In an update, the WHO said its Global Advisory Committee on Vaccine Safety (GACVS) reviewed the latest research on autism spectrum disorders (ASD) and vaccines, including concerns around thiomersal (thimerosal) and aluminium-containing adjuvants. The committee said the available evidence does not support a causal connection.
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Autism spectrum disorders, the WHO noted, describe a broad range of conditions marked by differences in social interaction and communication, along with patterns of behaviour such as difficulty with transitions, intense focus on details, or unusual sensory responses. Signs may appear early in childhood, but diagnosis can happen much later. Many autistic people also have other health conditions such as epilepsy, anxiety, depression or ADHD, and intellectual abilities can vary widely.
The committee’s latest analysis looked first at studies examining thiomersal-containing vaccines. Thiomersal is an organic compound that contains mercury and has been used for decades as a preservative in some medicines and vaccines to prevent contamination. WHO said evidence drawn from 31 primary research studies published between January 2010 and August 2025, covering data from multiple countries, strongly supports the safety of vaccines used in childhood and pregnancy and confirms the absence of a causal link with ASD.
GACVS also reviewed research on vaccines that use aluminium adjuvants, which are added to some vaccines to strengthen the immune response. The committee assessed studies from 1999 to March 2023, along with a large cohort study using nationwide registry data from children born in Denmark between 1997 and 2018. The conclusion was that high-quality evidence shows no association between the trace amounts of aluminum used in certain vaccines and autism, supporting continued use of these vaccines.
Following this review, the committee reaffirmed its earlier conclusions issued in 2002, 2004 and 2012: vaccines, including those containing thiomersal and/or aluminium, do not cause autism. WHO urged national authorities to base vaccine policies on the strongest available science and to address misinformation that can undermine public confidence.
The organisation also highlighted the wider impact of immunisation, calling it one of the most effective ways to prevent infectious diseases. Over the past 50 years, the WHO estimates vaccines against 14 diseases have saved at least 154 million lives and contributed to around 40% of the reduction in infant deaths.