Mercury, Thimerosal, and Vaccine Safety: What Research Is Underway?

Format: Fact Sheet
Institute: National Institute of Allergy and Infectious Diseases (NIAID)

Thimerosal is a preservative added to some vaccines that effectively kills bacteria and prevents contamination. When thimerosal is degraded or metabolized, ethyl mercury is produced. Unfortunately, there is limited information related to how ethyl mercury is handled by the body. Because of general concerns about mercury compounds, the U.S. Department of Health and Human Service agencies, including NIAID, were forced to use the guidelines for a similar compound, methyl mercury. Based on these guidelines, they determined that thimerosal should be reduced or eliminated in vaccines as a precaution. More research is needed to determine if the guidelines for methyl mercury are appropriate guidelines for thimerosal.

A new, easy-to-read fact sheet, NIAID-Supported Studies on Mercury, Thimerosal, and Vaccine Safety, is now available. This fact sheet provides answers to questions about NIAID-funded research to better understand what happens to thimerosal once it is introduced in the body.

Next Steps
Learn more about mercury, thimerosal, and vaccine safety by visiting www.niaid.nih.gov/factsheets/thimerosalqa.htm.