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.
These results suggest that there are differences in the way thimerosal and methyl mercury are distributed, metabolized, and excreted. Thimerosal appears to be removed from the blood and body more rapidly than methyl mercury.
Pichichero ME, Cernichiari E, Lopreiato J, and Treanor J. Mercury concentrations and metabolism in infants receiving vaccines containing thimerosal: a descriptive study. Lancet 360:1737-1741 (2002).
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.
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 121(2):e208-214 (2008).
Study III: Thimerosal Metabolism in Premature and Low Birth Weight Infants Receiving Routine Immunizations
NIAID conducted an additional study in Argentina that focused on 72 premature (32 to 37 weeks gestational age) and low birth weight (2,000 to more than 3,000 grams) infants.
Findings from the study indicate
- Results were consistent with earlier studies in infants of normal birth weight.
- Results were consistent with earlier studies in premature and low birth weight infants; mercury levels after vaccination can be predicted based on birth weight and amount of thimerosal in the vaccine.
- Mercury from thimerosal in vaccines is cleared from the infant’s body much more quickly than methyl mercury. Blood levels dropped to pre-vaccination levels within 30 days.
- Results confirm that methyl mercury is not an appropriate model to assess exposure or risk from thimerosal.
Pichichero ME et al. Mercury levels in premature and low birth weight newborn infants after receipt of thimerosal-containing vaccines. J Pediatr. 2009 Oct;155(4):495-9. Epub 2009 Jun 26.