We thank Dr. Dórea for his comments and agree that the issue of potential effects on children’s neuropsychological outcomes resulting from thimerosal exposures from vaccines is important. Unfortunately, it would be difficult to address this issue with the requisite level of rigor using the data collected as part of the New England Children’s Amalgam Trial.
In order to increase our ability to answer the question that motivated the trial, children were excluded if they already had a psychiatric diagnosis, including autism and related conditions. This exclusion criterion restricted the range of the outcomes of greatest concern with regard to thimerosal exposure.
More importantly, given that the youngest children enrolled in our trial were 6 years old, it would be difficult to get accurate information, retrospectively, on the thimerosal levels in the vaccine lots administered to these children years in the past. At the least, this would require access to medical records for each participant, a task that would be simplified if children in our trial had received all of their medical care from a small number of health maintenance organizations. This was not the case for our study sample, however, which was recruited from urban Massachusetts and rural Maine.
Under circumstances in which such an undertaking was possible, Thompson and colleagues1 used HMO records to quantify the vaccine-related thimerosal exposures of more than 1,000 children and found no evidence of adverse effects on neuropsychological function at 7 to 10 years of age.
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