A new report presented to the World Health Organization (WHO) reports that the WHO s decision in 2008 to endorse the use of thimerosal as a preservative for multidose childhood vaccines in the developing world is indeed scientifically valid. Some had previously claimed that there was a connection between thimerosal in vaccines and autism, but that link has since been debunked. And, as Dr. Michael Pichichero of the University of Rochester, the report s author, concludes, no new scientific evidence has raised concerns about the safety of thimerosal in vaccines.
In 1999, the FDA, the CDC and the American Academy of Pediatrics called for thimerosal to be removed from all vaccines sold in the U.S. out of precaution. This decision was based on an analysis indicating that, within the first year of life, children were exposed to levels of thimerosal from vaccines that exceeded recommended limits for another form of mercury, methylmercury which is known to be much more toxic than the ethylmercury in thimerosal. And so the U.S. subsequently switched from multi-dose to single-dose vaccines, which don t need a preservative and thus can be made without thimerosal. However, in the developing world, such a move would be so expensive as to deprive millions of infants and children from being vaccinated. Thus, in poorer regions of the globe, thimerosal continues to be used as a preservative for multi-dose vaccines.
For his review, Dr. Pichichero assessed a variety of studies on thimerosal. He found that one of the major flaws in the FDA s 1999 decision was the assumption that thimerosal and other forms of mercury act in the same way in the body. However, thimerosal is cleared much more quickly from the body than the mercury type that was analyzed by the FDA, and studies show that it does not accumulate in the bodies of children between vaccinations. All of the large, well-conducted epidemiologic studies on thimerosal have shown no association between thimerosal and autism; the only studies that suggested serious risks from thimerosal in vaccines had severe flaws that made the conclusions invalid. And if you need more evidence that thimerosal does not cause autism: Although thimerosal was removed from most vaccines in the U.S. following the FDA decision, the rate of autism in the country has continued to rise.
This is an incredibly important report, says ACSH's Dr. Gilbert Ross. Thimerosal does not cause neurological harm when used in vaccines, but many people remain unaware of its safety. Once again, in a global study, we see that the use of thimerosal in multi-dose vaccines is safe, and indeed necessary, in much of the developing world. The removal of this preservative from U.S. vaccines in 1999 at the behest of official health groups, due to nothing more than public fear and superstition, was a regrettable episode.