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Background It has been hypothesized that early exposure to thimerosal, a mercury-containing preservative used in vaccines and immune globulin preparations, is associated with neuropsychological deficits in children.
Methods We enrolled 1047 children between the ages of 7 and 10 years and administered standardized tests assessing 42 neuropsychological outcomes. (We did not assess autism-spectrum disorders.) Exposure to mercury from thimerosal was determined from computerized immunization records, medical records, personal immunization records, and parent interviews. Information on potential confounding factors was obtained from the interviews and medical charts. We assessed the association between current neuropsychological performance and exposure to mercury during the prenatal period, the neonatal period (birth to 28 days), and the first 7 months of life.
Results Among the 42 neuropsychological outcomes, we detected only a few significant associations with exposure to mercury from thimerosal. The detected associations were small and almost equally divided between positive and negative effects. Higher prenatal mercury exposure was associated with better performance on one measure of language and poorer performance on one measure of attention and executive functioning. Increasing levels of mercury exposure from birth to 7 months were 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.
Conclusions 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.
Source Information
From the Influenza Division (W.W.T., D.K.S.) and Immunization Safety Office (E.S.W., R.L.D.), Centers for Disease Control and Prevention, Atlanta; Abt Associates, Cambridge, MA (C.P., B.G., G.S.); Group Health Center for Health Studies, Seattle (P.B., J.D., L.A.J.); the Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care and Harvard Medical School, Boston (V.L.H., T.A.L.); Kaiser Permanente Division of Research and Vaccine Study Center, Oakland, CA (E.L., P.R.); UCLA Center for Vaccine Research, Torrance, CA (E.E., S.M.M.); Southern California Kaiser Permanente, Los Angeles (S.M.M.); RTI International, Atlanta (F.D.); and Stanford University, Palo Alto, CA (S.B.).
Address reprint requests to Dr. Thompson at the National Center for Immunizations and Respiratory Diseases, Influenza Division, Centers for Disease Control and Prevention, MS A32, 1600 Clifton Rd. NE, Atlanta, GA 30333, or at wct2{at}cdc.gov.
Related Letters:
Early Thimerosal Exposure and Neuropsychological Outcomes
Bernard S., Rooney J. P.K., Thompson W. W., Price C., DeStefano F.
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N Engl J Med 2008;
358:93-94, Jan 3, 2008.
Correspondence
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