Mercury Levels after Vaccination with Thimerosal-containing Vaccines
Abstract & Commentary
By Hal B. Jenson, MD, Chief Academic Officer, Baystate Health Professor of Pediatrics and Dean of the Western Campus of Tufts University School of Medicine, is Associate Editor for Infectious Disease Alert.
Dr. Jenson is on the speaker's bureau for Merck.
Synopsis: Increased mercury levels following vaccination with thimerosal-containing vaccines were detected in blood with a peak at 0.5 to 1 day post-vaccination. The half-life was 3.7 days, with return to prevaccination levels by 30 days post-vaccination.
Source: Pichichero ME, et al. Mercury levels in newborns and infants after receipt of thimerosal-containing vaccines. Pediatrics. 2008;121:e208-e214.
A prospective, observational study was conducted in Buenos Aires, Argentina, during 2003-2004 among 216 healthy infants > 32 weeks gestation who received age-appropriate immunizations, as routinely administered in Argentina. There were 3 groups: 72 newborns (group 1); 72 infants 2 months of age (group 2); and 72 infants 6 months of age (group 3). Total mercury levels were measure by atomic absorption in blood, stool, and urine samples taken before vaccination and, at one time, at a randomly assigned time point following vaccination. Half-life estimates were based on a 1-compartment, first-order pharmacokinetics model adjusted for the dosage of thimerosal in the vaccines and weight and age effects on volume and clearance.
Blood levels of mercury were detected at highest concentration in the samples immediately following vaccination. For groups 1, 2, and 3, respectively, the maximal mean + SD blood mercury levels were 5.0 ± 1.3, 3.6 ± 1.5, and 2.8 ± 0.9 ng/mL occurring at 0.5 days (group 1) to 1 day (groups 2 and 3) post-vaccination. Maximal mean + SD stool mercury levels were 19.1 ± 11.8, 37.0 ± 27.4, and 44.3 ± 23.9 ng/g occurring on day 5 post-vaccination. The blood mercury half-life was calculated to be 3.7 days for newborns, 2.0 days for 2-month-old infants, and 2.2 for 6-month-old infants; these half-lives were not significantly different. Blood mercury levels returned to prevaccination levels by 30 days post-vaccination.
Mercury as inorganic mercury was detected in most stool samples, and increased significantly after vaccination in all three groups. Mercury was not detected in urine. There was no elevation of urine GGT levels, a sensitive indicator of damage to proximal renal tubules.
Commentary
Thimerosal (sodium ethyl mercury thiosalicylate) has been used as a preservative in vaccines and other biologicals since the 1930s. Its antibacterial properties are attributed to the ethyl mercury that dissociates from the thimerosal molecule. The biology of ethyl mercury (CH3 CH2 Hg+) is poorly understood, and most exposure guidelines, such as from the US Environmental Protection Agency, are based on data of methyl mercury (CH3 Hg+). Both forms are readily transported to all tissues, and ethyl mercury has a shorter half-life.
In this study, mercury levels were relatively low in all age groups and were highest at 0.5 to 1 days post-vaccination. The increase in stool mercury in all three groups following vaccination suggests enterohepatic excretion of ethyl mercury, similar to methyl mercury. There was no evidence of urinary excretion, also similar to methyl mercury.
Based on the recommended childhood vaccination schedule in 1999, children in the United States could have potentially received up to 187.5 ug of ethyl mercury during the first 6 months of life from thimerosal-containing vaccines. This led to the recommendation in 1999 by the American Academy of Pediatrics that thimerosal be removed from all vaccines administered to infants in the United States. Because of the presence of ethyl mercury, the use of thimerosal in vaccines has been suggested by some, especially in the lay media and among anti-vaccine activists, to cause pervasive developmental disorders and autism, which has not been supported by epidemiologic studies. This study provides quantitative evidence of the perceived risk of thimerosal as a preservative in vaccines. The low, and very transient, levels of mercury found in this study are reassuring, and suggest that there is a very low risk, if any, for toxicity from mercury exposure from thimerosal-containing vaccines.
A prospective, observational study was conducted in Buenos Aires, Argentina, during 2003-2004 among 216 healthy infants > 32 weeks gestation who received age-appropriate immunizations, as routinely administered in Argentina.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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