A new study published in the September 27th New England Journal of Medicine does not support a link between early thimerasol exposure and neuropsychological deficits in children. Epidemiologist William V. Thompson, PhD, of the CDC’s National Center for Immunizations and Respiratory Diseases and others, conclude that:
Our study does not support a causal association between early exposure to mercury from thimerasol-containing vaccines and immune globulis and deficits in neuropsycological functioning at the age of 7 to 10 years.
1047 children between the ages of 7 and 10 were administed standardized tests assessing 42 neuropsychological outcomes (autism spectrum disorders were not assessed). The children were from four HMOs that participate in the Centers for Disease Control and Prevention’s Vaccine Safety Datalink. Researchers looked at exposure to mercury during the prenatal period, the neonatal period (birth to 28 days), and the first 7 months of a child’s life; they drew on computerized immunization records, medical records, personal immunization records, and parent interviews to determine exposure to thimerasol; interviews and medical charts provided information about potential confounding factors. Only a few significant associations between early exposure to mercury from thimerasol and neuropsychological outcomes were detected; all were small and “almost equally divided between positive and negative effects.” Specifically:
- Higher prenatal mercury exposure was associated with better performance on one measure of language; it was associate with poorer performance on one measure of attention and executive functioning.
- Higher levels of mercury exposure from birth to 7 months was associated with better performance on one measure of fine motor coordination and on one measure of attention and executive functioning.
- Increasing mercury exposure from birth to 28 days was associated with poorer performance on one measure of speech articulation and better performance on one measure of fine motor coordination.
The researchers noted these limitations regarding their study: only 30% of the subjects included for recruitment were enrolled; they did not control for interventions such as speech therapy; thimerasol exposure beyond 214 days was not assessed. These strengths were noted: the neuropsychological assessment used was similar to that used in the landmark studies of prenatal exposure to methyl mercury; children were enrolled based on their receiving vaccines, rather than on the basis of documented neurodevelopmental diagnoses; exposure information for both mothers and children was collected from a variety of sources. The study concludes:
The overall pattern of results suggests that the significant associations may have been chance findings stemming from the large number of statistical tests that we performed.
While the authors of the study clearly state its parameters and, too, its limitations, news sources and some autism organizations (those that claim that autism is really “mercury poisoning”) are packaging the study as about vaccines and autism, and suggest to what extent these are linked in the public consciousness.
- CDC study: Thimerosal doesn’t raise risk of neurological problems in kids
- Additive in Vaccines
(Star-Tribune, Twin Cities)
- Kids’ Vaccine Ingredient Not Likely Linked to Neurological Problems
- Report Focuses On Effects Of Vaccinations On Children’s Brains
(KXAN, Austin, Texas)
- Study Fails to Link Chemical, Brain Woes
- Vaccine Compound Is Harmless, Study Says, as Autism Debate Rages
(New York Times)
- Study rebuffs fears over mercury in vaccines
(Star-Ledger (New Jersey); I am quoted in this article)
Safe Minds, whose Executive Director, Sallie Bernard, was an external consultant and dissenting member of the study, put out a press release stating that the new study’s “draws a misleading conclusion.” But this statement is as “misleading” as the headlines cited above are about the study’s actual contents. This only furthers the belief that—no matter how clearly it is stated and shown that there is no causal association between early exposure to thimerasol and later neuropsychological outcomes—-a link between these has been firmly established in the public mind. And disputing that link will take more studies, more evidence, more efforts, and more self-scrutiny of why we believe what we believe.