NIAID-Supported Studies on Mercury, Thimerosal, and Vaccine Safety
Thimerosal is a preservative that has been added to some vaccines and other products because it is effective in killing bacteria and in preventing bacterial contamination. When thimerosal is degraded or metabolized, one product is ethyl mercury. In July 1999, U.S. Department of Health and Human Service (DHHS) agencies, including the National Institute of Allergy and Infectious Diseases (NIAID); The American Academy of Pediatrics; and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure and to reduce exposure to mercury from all sources. This decision was based on the various Federal guidelines for methyl mercury exposure and the assumption that the health risks from methyl and ethyl mercury were the same. More research is needed to determine if the guidelines for methyl mercury are also appropriate guidelines for thimerosal. NIAID thimerosal research focuses on better understanding what happens to thimerosal once it is introduced in the body and how this compares to current knowledge of methyl mercury pathways.