Vaccines and autism

Extensive investigation into vaccines and autism spectrum disorder has shown that there is no relationship between the two, causal or otherwise, and that vaccine ingredients do not cause autism. Major health authorities, including the World Health Organization, the National Health Service, the Centers for Disease Control and Prevention and the United States Food and Drug Administration, along with large-scale epidemiological research, reinforce the scientific consensus that vaccines are safe, that multiple concurrent vaccinations do not overwhelm the immune system, and that autism cannot be attributed to vaccination.

Scientist Peter Hotez researched the growth of the false claim and concluded that its spread originated with Andrew Wakefield's fraudulent 1998 paper, and that no prior paper supports a link. Despite the scientific consensus for the absence of a relationship, and the Wakefield paper's retraction, the anti-vaccination movement at large continues to promote theories linking the two.

Celebrity endorsements, social media campaigns and selective reporting have fuelled the anti-vaccination movement and public misunderstanding of vaccines. Fringe political actions continue to promote debunked claims. A developing tactic appears to be citing irrelevant or dubious studies to support a questionable claim.

Claimed mechanisms

The claimed mechanisms have changed over time, in response to evidence refuting each in turn. Anti-vaccine groups claim that specific vaccine ingredients can cause autism. Some of the most frequently mentioned ones are thiomersal, aluminium adjuvants and formaldehyde.