Do vaccines cause autism?
Written by AI from saved sources. A script checks every quote word for word, and a second AI compares each claim with its source. How we work and corrections
No: the evidence supports the conclusion that vaccines do not cause autism. Vaccines can have real side effects, and measles, mumps and rubella (MMR) vaccination can overlap with autism checks and diagnosis. That timing does not establish a cause.
Checked against: WHO, Cochrane, the Danish aluminium-vaccine study, October 2026.
Why people believe it
Wanting to understand vaccine risks is reasonable. The American Academy of Pediatrics’ (AAP) parent guide explains why some people worry. MMR vaccination and autism checks or diagnosis happen around the same age. It also recognises that parents want to understand risks and benefits.
The 1998 paper in The Lancet described 12 children who had been referred. Parents linked the start of behavioural symptoms to MMR in eight of the children, the paper reported. The Lancet fully retracted, or withdrew, the paper in February 2010. It cited false claims that the children were consecutively referred and that the investigations had ethics approval. The comparisons below examine whether MMR vaccination is linked to autism.
“The MMR jab triggers autism”
MMR stands for measles, mumps and rubella. WHO’s review reports a 2019 Danish study of 657,461 children. It found no overall link between MMR vaccination and autism. It also found no increased risk among children with autistic siblings or in the periods examined after vaccination. Its limitations included covering only one country and not reviewing individual medical records. They also included possible delays between symptoms and diagnosis.
Cochrane combined two observational studies. Together, they included 1,194,764 children. Cochrane found no evidence of a link between MMR vaccination and autism. It rated its confidence in that evidence as moderate.
“It’s the mercury”
FDA describes thimerosal as a mercury-containing preservative used to prevent the growth of harmful microbes in vaccines. WHO says MMR contains no preservative. WHO assessed 16 studies specifically on vaccines containing thiomersal and autism, alongside broader vaccine research. The best-designed original studies and all five reviews combining studies found no evidence supporting an autism link. This was true regardless of thiomersal content.
“What about aluminium?”
A 2025 Danish study compared aluminium exposure from vaccines in 1,224,176 children. It used national records and changes in vaccines’ aluminium content. The children were born in Denmark between 1997 and 2018. All were alive and living there at age two. Its public abstract, or summary, reports findings for 50 assessed disorders, including autism. It reports no link between greater exposure during the first two years and higher rates of these disorders. Individual medical records were not reviewed. Small relative effects, especially for some rarer disorders, could not be statistically excluded.
“Studies showing a link were ignored”
WHO considered eleven studies suggesting a link. It judged all to have major weaknesses, very low strength of evidence and high risk of bias. It gave greater weight to better-designed studies. Counting papers is not the same as weighing their reliability.
Thinking tool: after is not because
A diagnosis after a jab shows which came first, not what caused it. The Danish MMR study checked different periods after vaccination and children with autistic siblings. Neither showed increased risk.
Use it on other claims: ask what comparison would help separate timing from cause.
Official positions, with dates
On 20 November 2025, the American Academy of Pediatrics and other groups rejected a CDC website change. They also reaffirmed that there is no vaccine–autism link. On 11 December 2025, WHO’s vaccine-safety committee concluded that vaccines do not cause autism. This includes vaccines containing thiomersal or aluminium.
CDC’s Vaccine Safety page displays the date 22 July 2026. It claims that the statement “vaccines do not cause autism” is not evidence based because studies have not ruled out infant-vaccine causation. Its autism FAQ, or frequently asked questions page, displays the date 1 October 2026. It says studies continue to show that vaccines are not associated with autism. These are conflicting official statements; see the study findings above.
What people also ask
What are the possible side effects of getting vaccinated?
Cochrane reviewed MMR-related vaccine formulations, or versions. For those formulations, it found very small risks of fever-related seizures, or fits, around two weeks afterwards. It also found a very small risk of a blood-clotting disorder after MMR. The risk of this clotting disorder was smaller than after natural infection with the targeted viruses.
Are vaccines 100% safe?
No: the reviewed vaccines had the small risks described above. Cochrane also found no evidence of a link with autism.
Why are people worried about the MMR vaccine?
The AAP guide gives one explanation for some people’s concern. MMR vaccination and autism checks or diagnosis happen at overlapping ages.
What chemicals are linked to autism?
For the vaccine ingredients questioned here, WHO concludes that vaccines containing thiomersal or aluminium do not cause autism.
Check it yourself (5 minutes)
- Open Cochrane’s 2021 vaccine review.
- Find “certainty” and read the autism finding.
- Does Cochrane call its certainty absolute, moderate or low?
What you should have found
“Our certainty in the evidence for autism and febrile seizures was also moderate.”
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