Vaccines

Mercury Levels in Infants Receiving Routine Immunizations

Study I: Infant Metabolism of Thimerosal versus Methyl Mercury

NIAID-supported studies at the University of Rochester and the National Naval Medical Center in Bethesda, Maryland, assessed levels of mercury in the blood, hair, urine, and stool of 40 infants who received vaccines containing thimerosal and 21 infants who received vaccines without thimerosal as part of their routine immunization schedule. The infants studied were 6 months of age or younger. This study generated the following important results:

• Mercury levels in blood and urine were uniformly low in all infants studied and, in many cases, too small to measure. There was no observed dose-dependent relationship between the level of thimerosal received through vaccination and the level of mercury in the body.
• Mercury levels in blood did not exceed, at any time, the blood levels that correspond to Environmental Protection Agency guidelines for safe exposure to methyl mercury (based on continuous exposure).
• Mercury levels in the stool of infants receiving vaccines containing thimerosal were relatively high compared to mercury levels in the stool of infants who were not exposed to thimerosal, providing evidence that mercury from thimerosal is eliminated in the stool of infants.

Reference

Study II: Thimerosal Metabolism in Infants Receiving Routine Immunizations

NIAID conducted a follow-up of the Rochester study in Argentina with 216 newborns and infants. The purpose of this study was to:

• Measure blood levels of mercury in newborn, 2 month old, and 6 month old infants receiving thimerosal-containing vaccines as part of their routine care,
• Determine the excretion of mercury in feces,
• Expand the time points for sampling in a larger group of infants.

Results confirmed findings of the first study done at the University of Rochester.

• Blood mercury levels did not show accumulation between vaccinations in children; the levels drop to pre-vaccination levels within 30 days.
• Excretion of mercury in stools followed vaccination with thimerosal-containing vaccines.

Reference

Pichichero ME, Gentile A, Giglio N, Umido V, Clarkson T, Cernichiari E, Zareba G, Gotelli C, Gotelli M, Yan L, Treanor J. Mercury levels in newborns and infants after receipt of thimerosal-containing vaccines. Pediatrics (Non-government) 121(2):e208-214 (2008).

Study III: Thimerosal Metabolism in Premature and Low Birth Weight Infants Receiving Routine Immunizations

NIAID is also conducting an additional study in Argentina that focuses on premature (32 to 37 weeks gestational age) and low birth weight (2,000 to more than 3,000 grams) infants. Enrollment for this study is now complete.

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