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Immunization Science

Mercury Concentrations in Immunized Children

The article

Mercury concentrations and metabolism in infants receiving vaccines containing thiomersal: a descriptive study. Pichichero ME, Cernichiari E, Lopreiato J, Treanor J. The Lancet 2002;360(9347):1737-41.

The question

Do infants immunized with thimerosal-containing vaccines build up mercury in their bodies through their first months of life?

The study

Scientists at the University of Rochester Medical Center in New York measured the levels of mercury in blood, urine and stool of 2 and 6-month-old vaccinated infants. The researchers collected samples from 40 infants shortly after being immunized with thimerosal-containing vaccines. Twenty one infants immunized with thimerosal-free vaccines served as a control group. “All children remained healthy throughout the study and during 24-36 months of follow-up,” the researchers wrote.

The findings

Mercury levels were low in blood, undetectable in most of the urine samples, and high in stool samples. “Overall, the results of this study show that amounts of mercury in the blood of infants receiving vaccines formulated with [thimerosal] are well below concentrations potentially associated with toxic effects,” the researchers concluded.

The study also suggested that thimerosal amounts in these infants were eliminated through the stools within two weeks, the estimated blood half-life being only 7 days. “Coupled with 60 years of experience with administration of [thimerosal]-containing vaccines,” the researchers wrote, “we conclude that the thiomersal in routine vaccines poses very little risk to full-term infants, but that [thimerosal]-containing vaccines should not be administered at birth to very low birth weight premature infants.”

The relevance/bottom line

This study provides evidence that thimerosal-containing vaccines do not appear to contribute appreciably to mercury levels in the body and that ethylmercury is more rapidly eliminated than previously recognized.

NNii’s comment

This important study evaluated a small number of infants but should be reassuring to parents and others.