Is it safe to put mercury into vaccines?
Thursday March 18, 2004
Source: The Guardian
It appears so, although the waters were muddied this week by reports describing work by Mark Geier, a scientist who runs a private institution, the Genetic Centres of America, from his home in Maryland. Geier claimed that babies given a mercury-containing triple vaccine to protect against diphtheria, tetanus and whooping cough, were six times more likely to develop autism than those given a mercury-free alternative.
Mercury, in the form of a compound called thiomersal, has been added to a handful of different vaccines since the 1930s to prevent them from spoiling. While thiomersal is mostly found in combined diphtheria and tetanus vaccines, it is not added to MMR, polio or the BCG vaccine for tuberculosis.
Scientists have long known that mercury is toxic to brain tissue. When cases of autism were found to be increasing around the world, some blamed thiomersal.
But most scientists believe thiomersal is safe at the levels used in vaccines. A typical dose of a thiomersal-containing vaccine contains around 25 micrograms of mercury. "Mercury is a neurotoxin, so it does raise questions, but water is a neurotoxin too at high enough doses. If you're going to talk poison, you have to talk dose," says Karin Nelson, a child neurologist at the National Institute of Neurological Disorders and Stroke in Maryland. Nelson does not believe thiomersal causes autism, not least because the symptoms of mercury poisoning are quite different from those of autism. "No study has ever shown that children exposed to mercury in vaccines, or by any other route ... have more autism than children without such exposure," she says.