A new analysis adds to existing evidence showing that recommended childhood immunizations do not increase the risk of autism spectrum disorder (ASD).
Despite a 2004 review from the Institute of Medicine that concluded the measles, mumps, rubella, and thimerosal-containing vaccines don’t increase autism risk, concerns have persisted. Recent surveys indicate that about one-third of parents worry that their children receive too many vaccinations and that the cumulative effect of those vaccines may cause autism. At least 10% of parents refuse or delay vaccinations for their young children, believing it’s safer than following the Centers for Disease Control and Prevention’s (CDC) recommended vaccination schedule.
Because many parents’ concerns have focused on the number of vaccinations children receive, researchers at the CDC and Abt Associates of Bethesda, Md, calculated ASD risk based on the number of antibody-stimulating antigens that children are exposed to when they’re vaccinated. The study authors noted that even though the routine childhood immunization schedule includes more vaccines now than in the late 1990s, the amount of antigens in some vaccines has decreased substantially since then. For example, children who were fully immunized by age 2 years in 2012 were exposed to no more than 315 antigens. But in the late 1990s, fully immunized children were exposed to thousands of antigens.
The investigators used data from immunization registries and medical records to compare exposures to antibody-stimulating proteins and polysaccharides contained in vaccines in 256 children with ASD and 752 children without the disorder, all born between 1994 and 1999. They examined antigen exposures by the time the children were 3 months old, 7 months old, and 2 years old. Their analysis, published online today in the Journal of Pediatrics, showed no increased risk of ASD based on the number of vaccine-related antigens to which the children were exposed.
The authors noted that infants are exposed from birth to hundreds of viruses and other antigens in the environment. “It has been estimated that an infant theoretically could respond to thousands of vaccines at once,” they wrote. The likelihood that ASD is linked with childhood vaccinations “is not well supported by the known neurobiology of ASD, which tends to be genetically determined with origins in prenatal development,” they noted.