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Researchers have concluded that infants exposed to the highest levels of thimerosal, a mercury-laden preservative once found in many vaccines, were no more likely to develop autism than infants exposed to only a little thimerosal.

“Prenatal and early life exposure to ethylmercury from thimerosal in vaccines or immunoglobulin products does not increase a child's risk of developing autism," Dr. Frank DeStefano, senior study author and director of the immunization safety office at the Centers for Disease Control and Prevention, said in the study, released online in advance of the October issue of Pediatrics.

Researchers say the finding offers more reassurance to parents who worry that vaccinations will raise their child’s risk for autism.

According to USA Today, thimerosal first came under fire when the Food and Drug Administration speculated that the increased number of thimerosal-containing vaccines, including Hepatitis B, Hib (Haemophilus influenzae type B) and DTP (diphtheria, tetanus, pertussis) shots, may be exposing infants to too much mercury.

The FDA subsequently worked to remove thimerosal from the vaccinations. Currently, only trace amounts of the preservative, first added in the 1930s, remain in most injections.

The new study 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. Researchers determined the number of vaccinations and the amount of thimersol in them that each child was given and compared the effects it may have had. From prenatal age to 20 months, Children in the highest 10% of exposure were no more likely to develop autism than children in the lowest 10% of exposure.

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This isn’t the first time that a study found no clear correlation between autism and vaccination. Earlier this year, a study published in the Pediatric Infectious Disease Journal supported previous evidence that the Measles-Mumps-Rubella vaccine is not associated with an increased risk of autism. Research published in the Journal for Specialists in Pediatric Nursing in October 2009 also found no scientific link between childhood vaccines and autism. Both thimersol and the MMR vaccine were included in that research.

Finally, in February 2009, a U.S. federal court ruled that there was no scientific evidence linking vaccines to autism.

"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," Geraldine Dawson, chief science officer for a leading advocacy group, Autism Speaks, told USA Today in support of the new research. Dawson’s sentiments corroborates those of many physicians who also advocate vaccination.  

Others argue that parents should carefully consider whether or not to vaccinate their child since they don’t want any unknown or potentially harmful substances injected into their children’s bodies.

“Most support vaccination, but are concerned at - and question the necessity for - the large number of vaccines and the early ages at which these are given,” Dr. Richard Halverson said in a letter to the British Medical Journal published on the website of Generation Rescue, an Autism activism group that believes a link between vaccinations and the disease exists. “Many have studied the research, only to find - as I have - contradiction and uncertainty. They deserve to be treated with respect and given the opportunity for an open and honest debate.”

You can check out this MainStreet article for more on the existing debate about vaccinations.

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