In spite of all the anecdotes about autism-spectrum disorders and other neurological problems caused by vaccines, no scientific studies have shown a definitive link between the two. Yet many parents remain fearful. Why parents continue to question the safety of vaccines is the subject of an article just published in PLoS Biology, a peer-reviewed, open-access journal published by the Public Library of Science.
The article focuses on the research of a University of California-San Francisco medical anthropologist, Sharon Kaufman, PhD, who got interested in the persistent doubt around vaccines after reading reports of scientists, doctors, and government spokespeople receiving harassing phone calls and even death threats for simply reporting on findings that vaccines don't cause autism.
Much of the doubt was triggered by a 1998 British study published in The Lancet. It reported on a theory that the measles, mumps, and rubella (MMR) vaccine caused intestinal problems that released toxic substances into the brain. The paper was later discredited, and the author is currently under investigation for ethics violations.
At about the same time, a congressman in the U.S. had asked the Food and Drug Administration to review the use of thimerosal (a mercury-containing preservative) in all the products it regulates. The agency found that its current use could expose children under 6 months old to dangerously high levels, and as a result, asked pharmaceutical companies to remove it from vaccines. Since 2001, thimerosal preservatives have been largely eliminated from childhood vaccines (the flu vaccine being the one exception), although it's still detectable in trace amounts as a by-product of manufacturing.
Those two events were enough to generate serious doubt in parents' minds about the safety of vaccines, even though medical agencies around the world continued to publish papers and reviews disproving theories of a vaccine-autism link. Increasing access to the Internet didn't help either, Kaufman found, as collecting that information online led to more doubt.
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