Safe Minds and Mercury Policy Project Statement on "Mercury concentrations and metabolism in infants receiving vaccines containing mercury: a descriptive study"

Washington, DC, Nov. 29 -/E-Wire/-- According to Safe Minds and Mercury
Policy Project, few, if any, definitive conclusions can be drawn from this
latest thimerosal study.

"An initial analysis of the Pichichero et al. study of blood mercury concentrations in infants after vaccination with thimerosal-containing vaccines clearly demonstrates that this is a poorly designed study", said Sallie Bernard, president of Safe Minds.

Nevertheless, in the article and accompanying commentary, the authors make the following sweeping statements:

1. "Overall, the results of this study show that amounts of mercury in the blood of infants receiving vaccines formulated with thiomersal are well below concentrations potentially associated with toxic effects."
2. "Administration of vaccines containing thimerosal does not seem to raise blood concentrations of mercury above safe values in infants."
3. "This study gives comforting reassurance about the safety of ethyl mercury as a preservative in childhood vaccines."

"This report looks very much like agenda research and not an unbiased  study," said Michael Bender of the Mercury Policy Project.

According to the groups, these statements cannot be supported by the study design and results, for the following reasons.

        1. The blood mercury concentrations found in the study are not necessarily below the established safety limits: the authors cite a 1994 study by Grandjean to provide a safety level for methylmercury of 29 ppb (parts per billion) and state that this level is ten times lower than the mercury level needed to see a decrease in cognitive performance in children. However, this comparison does not utilize the latest safety data research. In 1998, Grandjean published an article (Grandjean et al., "Cognitive performance of children prenatally exposed to "safe" levels of methylmercury", Environmental Research, 1998) in which he rejected the conclusions of his earlier research and found performance declines when the average cord blood mercury  concentration was 59 ppb. His later study was validated as the "gold standard" by the National Academy of Science in their 2000 report "Toxicological Effects of Methylmercury" in which they found that the lowest dose for which adverse neurological effects are found is when cord blood is 58 ppb.

In the Pichichero study, there was one infant out of 33 (3%) in which blood mercury was measured who has a mercury concentration of 20.55 ppb. This infant was exposed to 37.5 micrograms of mercury, and the blood draw was taken on day 5. The authors state that the half life of ethylmercury is probably about 6-7 days. Thus, this infant's peak mercury concentration would be much higher than 20.55 ppb. Many infants in the 1990s were exposed to 62.5 micrograms of mercury at age 2 months, or nearly double what the study infant recieved. Therefore, it is probable that the blood levels of some infants given the full regimen of thimerosal vaccines in the 1990s would exceed the 58 ppb threshhold for adverse effects. THerefore, the results from the Pichichero study can hardly be seen as "reassuring" to any parent.

        2. Samples of blood were taken at various time points after exposure, but each study subject only had one apparent blood draw.  Standard study design for a parmacokinetic study, even a simple one, is to obtain multiple draws from each subject. Otherwise, it is not possible to make definitive statements about distribution, elimination, and half life, which this study seems to do.

           3. The reference point that they use to establish safety levels for thimerosal is methylmercury, a different compound than the ethylmerucry in thimerosal. Simply because a compound is similar does not mean it is as safe.

A good example is thalidomide, a sedative drug that was prescribed to pregnant women from 1957 into the early 60's. It was present in at least 46 countries under different brand names. When taken during the first trimester of pregnancy, Thalidomide prevented the proper growth of the foetus, resulting in horrific birth defects in thousands of children around the world. The reason is the Thalidomide molecule is chiral, with left and right-handed versions. The drug that was marketed was a 50/50 mixture. One of the molecules was a sedative, whereas the other was found later to cause foetal abnormalities.

The tragedy could have been avoided had the physiological properties of the individual thalidomide [molecules] been tested prior to commercialization. Molecules that look almost exactly alike can behave very differently.  The FDA is very rigid about testing the precise molecule being approved.

        4. The conclusions are based on blood draws from 33 exposed children, which is a small sample upon which to draw far reaching conclusions. It is also a convenience sample without random assignment of subjects and not even an attempt to make sure that comparison groups were age-sex matched.

        5. There was variability in the thimerosal doses given, and little attempt to incorporate dose differences in the half life model or safety assessment.

        6. With a claimed half life of 6-7 days, it is remiss that there is no collection within 3 days of exposure, when peak mercury levels would be obtained. It would be impossible to make any conclusions about safety without these measures.

For these reasons alone, Safe Minds and the Mercury Policy Project believe that the conclusions of this study should not be used in deliberations of thimerosal safety. Rather, more and better research is needed.

Mercury Policy Project


contact Sallie Bernard, Safe Minds, 908-295-6648/