A new WHO review has reaffirmed that childhood vaccines don’t cause autism, based on an examination of more than 25 years of studies scoping for possible linkages. 

There is no causal link, either, between vaccines containing preservatives such as thimerosal or aluminium and autism spectrum disorder (ASD), the review by the Global Advisory Committee on Vaccine Safety (GAVS), also found.

The findings, published Thursday, comes in the wake of a rash of statements by US Health and Human Services Secretary, Robert F. Kennedy Jr., reviving long dormant questions about a possible linkage. In March, Kennedy ordered the US Centres for Disease Prevention and Control (CDC) to conduct a review on the topic, which has not yet been completed. In November, he ordered the CDC to change language on its website reviving the long-debunked claims. 

The CDC website had previously stated that “studies have shown there is no link between receiving vaccines and developing autism spectrum disorder”.  Following the change, the site was updated to say that the claim “vaccines do not cause autism” is “not an evidence-based claim” – unleashing a wave of criticism from vaccine experts. 

New website text further says, “Scientific studies have not ruled out the possibility that infant vaccines contribute to the development of autism.”

However, another CDC page on thimerosal and vaccine safety, states that “research does not show any link between thimerosal in vaccines and autism, a neurodevelopmental disorder.”  It also points out, correctly, that the mercury-based preservative was removed from virtually all childhood vaccines decades ago.  Some flu vaccines still may contain thimerosal, also known as “thiomersal”.

The use of aluminium salts remains more common as adjuvants in vaccines such as those for hepatitis A, hepatitis B, diptheria, tetanus and pertussis (DTaP), and Human Papillomavirus (HPV).  But here, too, the WHO expert committee found no linkage between use of the adjuvant and autism.

Vaccines among the ‘most transformative’ inventions in history of humankind

The WHO review was published Thursday simultaneous to a WHO press briefing by WHO Director General Dr Tedros Adhanom Ghebreyesus.  

“Over the past 25 years, under-five mortality has dropped by more than half, from 11 million deaths a year to 4.8 million, and vaccines are the major reason for that,” Tedros told the end-year press briefing, organized with the UN press corps organization ACANU.

“Vaccines are among the most powerful, transformative inventions in the history of humankind,” the WHO Director General added, noting that they “save lives from about 30 different diseases, including measles, cervical cancer, malaria and more.”

Like all medical products, vaccines can cause side effects. “But autism is not a side effect of vaccines,” Tedros affirmed. 

The WHO Expert Committee reviewed 31 new studies in multiple countries produced over the past 15 years examining associations between vaccines containing thiomersal and aluminium adjuvants and autism, as well as the association between vaccines and autism in general. It was the first such review since 2012.

“The committee concluded that the evidence shows no link between vaccines and autism, including vaccines containing aluminium or thiomersal,” Tedros declared.

“This is the fourth such review of the evidence, following similar reviews in 2002, 2004 and 2012. All reached the same conclusion: vaccines do not cause autism,” Tedros concluded.

He said that the new study reached the same findings as similar reviews in 2002, 2004 and 2012 – capturing evidence over some 25 years. 

Bucking national pressures

Since taking office earlier this year, Kennedy has not only revived debunked theories about a link between vaccines and autism, but he has also reduced US support for global polio vaccine efforts and lashed out at Gavi, the Vaccine Alliance about its DPT vaccination strategies. Just last week, recently a new CDC vaccine advisory committee packed with handpicked vaccine skeptics recommended against newborn vaccination against hepatitis B – another decision decried by experts. (See related story).

CDC Committee Delays Hepatitis B Vaccine for Newborns in Critical Guidelines Shift

In terms of any link between vaccines and autism, not only the WHO Vaccine Expert Committee, but numerous other advisory groups from around the world have come to the same conclusion regarding the lack of any linkage between vaccines and autism, WHO’s Katherine O’Brien, a senior vaccine expert, told the press briefing. 

“Not only when WHO has undertaken evidence reviews, but numerous advisory bodies around the world have consistently come to the same conclusions about the lack of risk of thimerosal or aluminium related to the autism questions,” O’Brien said. 

“And in particular, we develop our recommendations through external committees of experts who are drawn from around the world so that they can provide advice, and again, an independent review of the argument in order to assist the process of developing recommendations.” 

Asked whether WHO had been under pressure to changes its position due to the new US stance that the linkage between vaccines and autism remained an open question, Tedros said:  

“We disagree. We disagree respectfully, and we say no, because this is a science based organization, and science has to be respected.”

While he regrets the US decision to withdraw from WHO as of January, 2026, ressures from member states are nothing new Tedros added, saying, “I can give you many examples from the US, China, Russia and others.”   

Image Credits: UNICEF/Pakistan , HHS.