MONDAY, Sept. 13 (HealthDay News) -- Infants exposed to the
highest levels of thimerosal, a mercury-laden preservative that
used to be found in many vaccines, were no more likely to develop
autism than infants exposed to only a little thimerosal, new
The study offers more reassurance to parents who worry that
vaccination raises their children's risk for autism, the
"Prenatal and early life exposure to ethylmercury from thimerosal in vaccines or immunoglobulin products does not increase a child's risk of developing autism," concluded senior study author Dr. Frank DeStefano, director of the immunization safety office at the U.S. Centers for Disease Control and Prevention.
The study was released online Sept. 13 in advance of publication
in the October print issue of
Thimerosal has been used as a preservative in vaccines since the
1930s, according to background information in the article.
Concerns about the chemical began to crop up in 1999, when the
U.S. Food and Drug Administration said that because of the
increased number of thimerosal-containing vaccines added to the
infant vaccination schedule, infants may be exposed to too much
mercury. Thimerosal used to be found in hepatitis B, Hib
(Haemophilus influenzae type B) and DTP (diphtheria, tetanus,
pertussis) vaccines, among others.
During the ensuing years, the FDA worked with manufacturers to
eliminate thimerosal from vaccines, according to the agency's Web
site. Today, thimerosal has been removed or reduced to trace
amounts in all vaccines routinely recommended for children 6 years
of age and younger, with the exception of inactivated seasonal flu
vaccine, according to the FDA. Parents who are concerned about
thimerosal can ask for a preservative-free version, DeStefano
And thimerosal wasn't the only proposed autism-vaccine link. A
1998 paper in
The Lancet suggested the MMR (measles-mumps-rubella) vaccine
might trigger autism. The journal later retracted the paper, and
numerous studies have refuted any link between the MMR vaccine and
In February of 2009, a U.S. federal court ruled that there was
no scientific evidence linking vaccines to autism.
In the new study, researchers examined medical records and
conducted interviews with the mothers of 256 children with an
autism spectrum disorder and 752 children matched by birth year who
did not have autism. The children were all members of three health
care management organizations in California and Massachusetts.
Researchers also gathered information about the manufacture and
lot number of the vaccines that the children received, to determine
how much thimerosal they were likely exposed to.
Children in the highest 10 percent of thimerosal exposure,
either prenatally or between infancy and 20 months, were no more
likely to have autism, an autism spectrum disorder or autism
spectrum disorder with regression than children in the lowest 10
percent of exposure.
"This study adds to a large body of evidence indicating that early thimerosal exposure through vaccination does not cause autism," said Geraldine Dawson, chief science officer for a leading advocacy group, Autism Speaks. Dawson was not involved with the research.
She urged parents to have their children vaccinated.
"We encourage parents to have their children vaccinated and to establish a trusting relationship with their child's pediatrician so they can discuss any concerns they have," Dawson said.
The U.S. Food and Drug Administration has more on
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