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.
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.