The claim that vaccination causes autism has been one of the most persistent vaccine controversies of the last three decades. The strongest current evidence does not support a causal link between vaccines and autism.
Where did the claim come from?
Public concern intensified after a 1998 paper suggested a possible association between MMR vaccination and developmental disorders. The paper was later retracted, and subsequent large studies in different populations did not reproduce a causal relationship.
What does more recent evidence show?
WHO's 2025 review considered 31 primary studies published between 2010 and August 2025, alongside evidence concerning thiomersal and aluminium-containing vaccines. Its expert committee reaffirmed that the available high-quality evidence does not show a causal relationship between vaccines and autism spectrum disorder.
What about vaccine ingredients?
Claims have also focused on thiomersal and aluminium salts. WHO's current vaccine-safety guidance says extensive research has not found these vaccine constituents to cause autism. A large Danish cohort study reviewed by WHO also found no association between early-childhood exposure to aluminium-adsorbed vaccines and a range of chronic disorders, including autism.
Why does the claim persist?
Timing can be persuasive: signs of autism often become apparent during childhood, which overlaps with the period when routine vaccines are given. A sequence in time, however, does not establish that one event caused the other. Establishing causation requires comparing vaccinated and unvaccinated or differently exposed populations while accounting for other explanations.