Vaccines don't cause autism
Large studies across countries show that vaccines do not cause autism. The evidence covers MMR, thimerosal and aluminum. A diagnosis after vaccination does not establish a cause; reliable comparisons show whether autism is more common among vaccinated children.
On this page
Large studies have tested the claim
WHO’s 2025 assessment again found no causal link between vaccines and autism. The MMR review’s autism analysis included two observational studies totaling 1,194,764 children. Its result agrees with the broader evidence; it is not a randomized trial of every vaccine.
Children with an autistic sibling were studied too
A US study followed 95,727 children with older siblings. It found no increased autism risk linked to MMR, including among the 1,929 children with an autistic older sibling. The smaller sibling group leaves more uncertainty, and the study cannot answer every question about rare medical conditions.
Ingredient versions have also been studied
Thimerosal and aluminum are different substances. Evidence does not support either as a cause of autism. A Danish cohort studied cumulative vaccine aluminum and chronic outcomes in 1,224,176 children. It is observational, with a corrected supplement and limits for rare outcomes—not proof of zero risk from every vaccine.
A sequence of events does not establish a cause
Developmental changes may become noticeable around routine vaccination ages. Families’ observations deserve attention, but timing alone cannot explain the cause. Researchers compare groups and results across studies. Autistic people have different strengths and support needs; developmental concerns deserve assessment regardless of vaccination.
The actual formulation matters
The cited M-M-R II label lists no aluminum, thimerosal or formaldehyde. That statement concerns this formulation. It should not be generalized to every product worldwide or treated as the only reason the autism claim fails.
Safety and side effects
Finding no autism link does not mean vaccines have no adverse effects. The MMR page explains its known side effects; the ingredients page covers ingredient-specific reactions and evidence.
Large studies across countries show that vaccines do not cause autism.
Keep in mind
- The findings apply to the vaccines, populations and outcomes studied. Personal recommendations depend on your health and current local guidance.
Sources you can check
Publication links open in a new tab, so you can keep your place here.
Statement of the WHO Global Advisory Committee on Vaccine Safety (GACVS) on vaccines and autism (opens in a new tab)
WHO, 2025
Assesses vaccine–autism evidence, including thimerosal and aluminum; this is not a finding of zero vaccine side effects.
Return to reading ↑Vaccines for measles, mumps, rubella, and varicella in children (opens in a new tab)
Cochrane, 2021
Reviews effectiveness and harms in children. Different outcomes use different studies and participant totals.
Return to reading ↑Aluminum-Adsorbed Vaccines and Chronic Diseases in Childhood: A Nationwide Cohort Study (opens in a new tab)
Annals of Internal Medicine, 2025
Danish observational cohort of 1,224,176 children. Its supplement was corrected; rare-outcome uncertainty remains.
Return to reading ↑M-M-R II — Prescribing Information (opens in a new tab)
FDA
Ingredient and manufacturing information for this formulation, not every MMR product worldwide.
Return to reading ↑Measles, Mumps, Rubella (MMR) Vaccine Safety (opens in a new tab)
CDC
Explains known MMR side effects; combined MMRV has a different seizure-risk comparison.
Return to reading ↑Aluminium adjuvants in vaccines and potential health effects: systematic review (opens in a new tab)
BMJ, 2026
59 studies with uneven evidence quality. Recognizes uncommon persistent local reactions and gaps for rare or delayed outcomes.
Return to reading ↑Autism Occurrence by MMR Vaccine Status Among US Children With Older Siblings (opens in a new tab)
JAMA, 2015; corrected 2016
The study used US insurance records. Some parents may have delayed vaccination after developmental concerns. Smaller groups, including children with an autistic sibling, leave more uncertainty.
Return to reading ↑
Detailed research notes and source data
Our longer notes explain how we checked the studies, including disagreements and documents we could not get.
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These pages have not completed expert review. For personal vaccine advice, talk to a clinician who knows your circumstances.
Research checked: . Wording reviewed: 2026-10-15. Version: vaccine-2026-10-15.
We revisit the page when new evidence or corrections change the answer. A public history of corrections is not available yet.