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Officials Defend Safety of Vaccines for Kids

No Evidence of Link Between Thimerosal Preservative and Autism, Health Officials Say
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WebMD Health News

July 19, 2005 -- U.S. health officials defended the safety of childhood vaccines Tuesday in an apparent attempt to answer vocal critics questioning the connection between some vaccines and autism.

Officials told reporters that they are worried that concerns over possible connections between autism and the mercury-containing preservative thimerosalconcerns over possible connections between autism and the mercury-containing preservative thimerosal are discouraging parents from vaccinating children against a host of infectious diseases.

Their arguments, timed a day before autism and antivaccine activists are scheduled to attend a rally on Capitol Hill, break down along a familiar line: there is no evidence vaccines containing mercury are a direct cause of autism, though the science is still somewhat spotty. And even if some connection is found in the future, the benefits of vaccines in preventing more than a dozen potentially deadly diseases far outweigh the risks.

"The science tells us very clearly that vaccines save lives and protect our children," CDC Director Julie M. Gerberding, MD, told reporters.

Gerberding and other officials stress that childhood vaccines have virtually erased diseases like polio, diphtheria, and measles, that once killed thousands of U.S. children. But such diseases remain common in developing countries where vaccination rates are low, meaning that they continue to pose a potential threat in the U.S.

Rise in Autism Rates

At the same time, scientists still don't know what has caused the rise in diagnosed autism cases over the past 20 years. Between 2 and 6 per 1,000 children born in the U.S. are diagnosed with autism, putting the overall prevalence as high as one in every 163 children.

Some blame the rise on thimerosal, a mercury-containing chemical that was used as a vaccine preservative in childhood vaccines until 2001. The chemical is still used in influenza vaccines and exists in trace amounts in others because manufacturers continue to use it to disinfect equipment.

Public concern over thimerosal has spurred vaccine makers to try to minimize its use. The preservative is needed in multidose vaccine vials, such as the flu vaccine, forcing manufacturers to switch to single-dose vials to avoid using it.

The CDC has signed a contract to purchase 3.5 million doses of preservative-free flu vaccine from manufacturer Sanofi-Pasteur, Gerberding told a House committee in May. The company is expected to make another 3 million to 5 million thimerosal-free doses.

"We are very, very concerned that people have confidence in the products that they use," said Murray Lumpkin, MD, acting deputy commissioner of the FDA.

A 2004 report from the Institute of Medicine rejected any link between thimerosal-containing vaccines and autism.

Thimerosal Legislation

Still, many researchers are troubled by evidence that a rise in autism rates appeared to roughly coincide with the use of the chemical in the vaccine supply.

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