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Children's Vaccines Health Center

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Vaccine FAQ

Vaccine Benefits, Vaccine Risks: 10 Basic Questions Answered

3. Some autism advocacy groups say vaccines -- especially those that contain the mercury-based compound thimerosal -- can cause autism and brain damage. They are sincerely worried. Why shouldn't I believe them?

"Autism is a serious and very challenging disease for families to cope with," says Schuchat. "Parents want explanations of how this happened to their child. lt is important for us to support research and programs that will help us better understand the factors that lead to autism and to find the best treatments. But a very large number of scientific studies have been carried out, and extensive scientific reviews, that have concluded there is no causal connection between vaccines or the preservative thimerosal and autism.

"There are hundreds of studies that have looked one way or another at these issues. Some are animal studies, some are toxicology studies, and some are human studies with a number of different designs. There have been efforts to review the evidence, the direct human evidence and the indirect animal evidence. Those reviews don't just look at the last sentence in the article but look at the study methods and ask if the methods and the results justify the conclusions. [The most recent] extensive review was carried out by the Institute of Medicine with a number of experts and concluded the information from all of these studies taken together did not support a causal association [between vaccines and autism].

"They concluded that other factors or explanations for autism should be sought. And more recently, people have thought that genetic and some environmental research may be more promising than continuing to pursue thimerosal."

(Do you think the MMR vaccine causes autism? WebMD's Rod Moser, PA, PhD, and Steven Parker, MD, both say "no." Find out why on their blogs. )

4. If only to err on the side of caution, why can't all vaccines be thimerosal-free?

"The vaccines that are given to children in the U.S. are nearly thimerosal free," says Schuchat. "All but the flu vaccines that are given to young children do not contain thimerosal. Some formulations of flu vaccine are thimerosal-free and some are not. So the pediatric vaccine supply is nearly thimerosal-free. Thimerosal is a preservative that keeps germs from overgrowing. So vials of vaccine that are multiple doses, 20 or 30 doses, have a preservative to keep them from bacterial contamination. It was put in there because people died from vaccines that were contaminated.

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