FRIDAY, March 29 (HealthDay News) -- Although some parents worry
about the sheer number of vaccines babies typically receive, a new
U.S. government study finds no evidence that more vaccinations
increase the risk of autism.
Looking at about 1,000 U.S. children with or without autism,
researchers at the Centers for Disease Control and Prevention found
no connection between early childhood vaccinations and autism
Children with autism and those without had the same total
exposure to vaccine antigens -- the substances in vaccines that
trigger the immune system to develop infection-fighting
"This should give more reassurance to parents," said lead researcher Dr. Frank DeStefano, director of the CDC's Immunization Safety Office.
The findings, which appear online March 29 in the
Journal of Pediatrics, cast further doubt on a link between
vaccines and autism spectrum disorders -- a group of developmental
brain disorders that impair a child's ability to communicate and
The first worries came from a small British study in 1998 that
proposed a connection between the measles-mumps-rubella (MMR)
vaccine and autism. A spate of research since has found no link,
and the original study was eventually retracted by the
Lancet, the journal that published it.
Then came concerns about thimerosal, a preservative once used in
certain childhood vaccines (but never MMR) that contains small
amounts of ethyl mercury. Again, international studies failed to
show a link to autism.
More recently, worries have shifted to the notion that children
are getting "too many vaccinations, too soon." In the United
States, children can be immunized against 14 different diseases by
the time they are 2.
DeStefano said his team focused on antigen exposure, rather than
just the number of vaccinations, because that gives a more precise
idea of the "immune system stimulation" kids received through
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
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
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
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 autism symptoms in a genetically and medically
Both Offit and DeStefano stressed that there is no reason for
parents to delay vaccinating their child.
"This is one more piece of evidence to help reassure parents," Offit said.
The American Academy of Pediatrics has information on
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