The article leads a reader to conclude that no matter how many scientific studies fail to find a causal link between thimerosal to neurological disorders (and The New England Journal publishes the latest study in the same issue), the scientific and medical establishment will continue to face questions, criticisms and doubts on this issue.
In "Thimerosal and Vaccines—A Cautionary Tale," Dr. Paul A. Offit, chief of the Division of Infectious Diseases at Children's Hospital of Philadelphia, notes that the public took little notice of an amendment in the November 1997 bill reauthorizing the Food and Drug Administration, which required the FDA to "compile a list of drugs and foods that contain intentionally introduced mercury compounds and [to] provide a quantitative and qualitative analysis of the mercury compounds in the list." Offit explains:
Eighteen months later, in May 1999, the FDA found that by 6 months of age, infants could receive as much as 75 µg of mercury from three doses of the diphtheria–tetanus–pertussis vaccine, 75 µg from three doses of the Haemophilus influenzae type b vaccine, and 37.5 µg from three doses of the hepatitis B vaccine — a total of 187.5 µg of mercury. The use of mercury in vaccines wasn't new; thimerosal, an ethylmercury-containing preservative, had been used to prevent bacterial contamination since the 1930s.
To determine whether the amount of mercury in vaccines was safe, FDA scientists examined safety guidelines from three sources: their own agency, the Environmental Protection Agency, and the Agency for Toxic Substances and Disease Registry. They found safety guidelines for methylmercury (environmental mercury), but not for ethylmercury (thimerosal). Although these two molecules differ by only one carbon atom, the difference isn't trivial. Ethylmercury is excreted from the body much more quickly than methylmercury and is therefore much less likely to accumulate. For this reason, the safety guidelines that had been established for methylmercury weren't likely to be predictive of the safety of ethylmercury.
In mid-June 1999, FDA scientists held a meeting to discuss their findings. Present were representatives from the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) — the organizations that are principally responsible for making vaccine recommendations for U.S. children. Several attendees left the meeting concerned that infants might be receiving too much mercury from vaccines. Although they were largely reassured by studies of children who had ingested large quantities of mercury from fish in their diet, they couldn't find a single study that compared neurologic outcomes in children who had received thimerosal-containing vaccines with those in children who had not.
On July 9, 1999, after much wrangling, the CDC and AAP decided to exercise the precautionary principle. They asked pharmaceutical companies to remove thimerosal from vaccines as quickly as possible; in the interim, they asked doctors to delay the birth dose of hepatitis B vaccine in children who weren't at risk for hepatitis. A press release issued by the AAP revealed the ambivalence among its members: "Parents should not worry about the safety of vaccines," it read. "The current levels of thimerosal will not hurt children, but reducing those levels will make safe vaccines even safer. While our current immunization strategies are safe, we have an opportunity to increase the margin of safety." Critics wondered how removing something that hadn't been found to be unsafe could make vaccines safer. But many parents, frightened by a sudden change in policy, reasoned that thimerosal was targeted because it was harmful — and their faith in the vaccine infrastructure was shaken. Doctors were also confused by the recommendation.
So what does all this mean? It suggests that doctors who were in a position to give advice about the safety of vaccines faced a moment when they had to try to communicate to the public both their vigilance on the matter of mercury contained in the vaccine preservatives and to express reassurance about the safety of an essential public health vaccination program. In retrospect, it reads like a very difficult challenge to communicate both ideas at the same time.
And, Offit notes, the pediatricians made a difficult situation worse with their ambivalent words. "The thimerosal controversy should stand as a cautionary tale of how not to communicate theoretical risks to the public; otherwise, the lesson inherent in the collateral damage caused by [thimerosal's] precipitous removal will remain unlearned."
Even if you disagree with Offit's characterization that removing thimerosal from vaccines is precipitous, it's likely that you can understand why vaccines are an issue fraught with emotion and tension for the autism community searching for answers, understanding and causes for their loved one's condition.
Policy makers and the research establishment seem to understand this, too. And so the medical community continues researching the issue. You can read the abstract to the latest study, by William W. Thompson Ph.D. and 17 other researchers with CDC backing publishing a study in the same issue of The Journal titled, "Early Thimerosal Exposure and Neuropsychological Outcomes at 7 to 10 Years" which looked at 1,047 kids and found 42 with neuropsychological conditions (without assessing whether any had autism spectrum disorders). It concludes: "Our study does not support a causal association between early exposure to mercury from thimerosal-containing vaccines and immune globulins and deficits in neuropsychological functioning at the age of 7 to 10 years."
This result echoes some other studies, but the trouble is that trust is hard for some advocates to find. And the voices of parents who distrust the research establishment don't hesitate to launch critiques. Cindy Waeltermann, director of AutismLink.com, an advocacy group which has opened an autism services center in Pittsburgh, criticized the researchers for not assessing whether the 42 kids with abnormalities detected had autism, and added:
The study assessed ONLY those children who were exposed to mercury during the first 28 days to 7 months of life. The autism community has always asserted that autism is caused by a build up of mercury in the system as a result of multiple vaccinations over the first two years of life. This study did not address this hypothesis. ... The CDC, which is supposed to be the quintessential research organization of modern times has once again proven its fallibility.... This study was geared to a particular outcome before it even began.
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