A recent survey found that about one-third of parents thought children receive too many vaccinations in their first two years of life, and that the shots could contribute to autism.
But there's no scientific evidence of that, said Dr. Paul Offit, chief of infectious diseases at the Children's Hospital of Philadelphia.
He said it's understandable that parents might worry. "You see your baby receiving all these vaccines. It looks like too much. It feels like too much," Offit said.
But, he said, there's no biological basis for the idea that vaccines "overstimulate" the immune system, and that somehow leads to autism.
Every day, babies' immune systems battle many more antigens than are present in vaccines, DeStefano explained. "Most infants can handle exposure to many antigens," he said.
The findings are based on 256 children with an autism spectrum disorder and 752 autism-free kids who were matched to them based on age, sex and health insurance plan.
The CDC team found that kids' total antigen exposure in the first two years of life was unrelated to their risk of developing an autism disorder.
That was also true when they considered babies' antigen exposure in the first three months of life, and the first seven months. Nor was there any connection between autism risk and the amount of vaccine antigens children received on any single day.
"This provides evidence that concerns about immune system overstimulation are unfounded," DeStefano said.
Geraldine Dawson, chief science officer for the advocacy group Autism Speaks, said the study "adds to the existing literature showing no connection between vaccines and autism in large epidemiological studies."
She added, though, that further research is needed "to explore whether, in rare cases, a genetic vulnerability might increase susceptibility to vaccine-related side effects, including the triggering of autis
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