Primary Review
Twenty epidemiologic studies have shown that neither thimerosal nor MMR vaccine causes autism. These studies have been performed in several countries by many different investigators who have employed a multitude of epidemiologic and statistical methods. The large size of the studied populations has afforded a level of statistical power sufficient to detect even rare associations. These studies, in concert with the biological implausibility that vaccines overwhelm a child’s immune system, have effectively dismissed the notion that vaccines cause autism. Further studies on the cause or causes of autism should focus on more-promising leads¹.
Cochrane Analysis
One of the largest multi-study analysis ever conducted saw 138 studies with more than 23 million children. Fifty-one studies (10 million children) assessed how effective the vaccines were at preventing the diseases, and 87 studies (13 million children) assessed unwanted effects. In this 2020 update, we have included 74 new studies published since 2012.
The review concluded that MMR, MMRV and MMR+V vaccines are effective in preventing the infection of children by measles, mumps, rubella and chickenpox, with no evidence of an increased risk of autism or encephalitis and a small risk of febrile seizure.
Reference
¹Gerber JS, Offit PA. Vaccines and autism: a tale of shifting hypotheses. Clin Infect Dis. 2009;48(4):456-461. doi:10.1086/596476https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908388/
²Cochrance Review: Does the measles, mumps, rubella and varicella (MMRV) vaccine protect children, and does it cause harmful effects? https://www.cochrane.org/CD004407/ARI_does-measles-mumps-rubella-and-varicella-mmrv-vaccine-protect-children-and-does-it-cause-harmful