A comprehensive study published in the September 27, 2007 edition of the New England Journal of Medicine 1 has demonstrated “no causal association” linking exposure to a mercury-based preservative used in routine childhood vaccines to abnormalities in later neuropsychological development.
The preservative, known as thimerosol, is approximately 50% (by weight) mercury and had been used as a preservative in a number of biological preparations since the mid 1930s.
In the recent study, a team headed by William Thompson, PhD of the US Centers for Disease Control and Prevention administered a battery of 42 neuropsychological tests to a panel of 1,047 children aged 7 to 10 years at the time of the examinations. Exposure to thimerosol was determined from vaccination records and/or the recollections of each child’s parent.
The study found that there were very few associations between thimerosol and the results of the neuropsychological tests, with both positive (better than expected performance) and negative (less than expected) associations being equally present. This was in contrast to reports from 3 previous studies in which 1 study found that there was a slightly higher association of lower scores on neuropsychological among children that had received vaccines containing thimerosol, 1 study found a slightly lower association, and a study that found no relationship.
The authors of the study were quick to point out that they did not specifically address the question of a possible causal link between thimerosol and autism or “autism spectrum disorder,” leaving that question to be answered by ongoing studies specific to that topic.
In related commentary published in the same issue of the New England Journal, 2 Paul Offit, chief of the Division of Infective Diseases at the Philadelphia (PA) Children’s Hospital reviewed the history of the thimerosol controversy and stressed that the decision of the US Food and Drug to ask vaccine makers to investigate whether alternatives to thimerosol could be used and to voluntarily cease thimerosol use when such alternates were proven safe.
Dr. Offit also noted that the report’s findings will probably meet with a chorus of protest from those who have, in the absence of scientific evidence, attempted to link thimerosol to autism for reasons involving potential financial or political gains.
“Despite several years of reassuring studies, the thimerosol controversy continues to be emotionally charged. Physicians, scientists, government policy advisors, and child advocates who have publicly stated that vaccines don’t cause neurologic problems or autism have been harassed, threatened, and vilified, receiving hate mail and occasionally death threats. The CDC, in response to planned protests at its gates, recently beefed up security and instructed personnel about how to respond if physically attacked.”
Commentary
Normally, at this point, I would present some additional commentary or personal observations on the topics mentioned above. I will not do so simply because most people have already made up their minds on these issues and no amount of evidence will be sufficient to force a change.
For those readers interested in reading a balanced and impartial review of the ongoing legal controversy regarding vaccines and autism, see Stephan Sugarman’s “Cases in Vaccine Court – Legal Battles over Vaccines and Autism” in the same issue of the New England Journal. 3
For those who have decided the issue, based on their own prejudices and/or motivations, I ask only that you be honest with yourselves.
Notes
1. Thompson, William W; Price, Cristofer; Goodson, Barbara; Shay, David K, and Benson, Patti et al. Early Thimerosal Exposure and Neuropsychological Outcomes at 7 to 10 Years, NEJM (September 27, 2007) 357: 13, 1281-1292.
2. Offit, Paul A. Thimerosal and Vaccines — A Cautionary Tale, NEJM (September 27, 2007) 357: 13, 1278-1279.
3. Sugarman, Stephen D. Cases in Vaccine Court – Legal Battles over Vaccines and Autism, NEJM (September 27, 2007) 357: 13, 1275-1277.
