More Vaccines
Without Thimerosal as a Preservative
Several manufacturers announced that they will be offering additional
vaccines that do not contain thimerosal as a preservative.
Haemophilis Influenzae Type b Vaccine: Wyeth Lederle Vaccines, the manufacturer of the last remaining Hib vaccine containing thimerosal as a preservative, announced that they would no longer market the multi-dose vaccine as of July 2000. While this is good news in the prevention of thimerosal exposure, vaccine sold in June and July 2000 will be used for many months prior to the expiration.
Diphtheria Tetanus and Acellular Pertussis Vaccine: The only DTaP vaccine that does not contain thimerosal as a preservative available in the U.S. is the SmithKline Beecham product, Infanrix. However, other manufacturers outlined plans to remove this preservative from their products over the next 1-2 years. Also, SmithKline Beecham and Aventis Pasteur announced that they hope to have new combination products that include DTaP available in early 2001 that do not contain thimerosal as a preservative. At that time, there will no longer be any vaccines used on a routine basis for infants under 6 months of age that contain thimerosal as a preservative. Some vaccines will have trace amounts that are not biologically significant.
Studies on
mercury-exposure in children
Two studies were discussed which had very different outcomes
Preliminary data from a CDC Vaccine Safety Data Link study indicated a weak, but statistically significant, association between cumulative exposure to mercury from vaccines and tics, attention deficit disorder, language and speech delay, and a non-specific compilation of neurodevelopmental delays. No associations were found with other neurological disorders or renal disease.
The abnormalities that were significantly associated with mercury exposure have been found at increased frequency in long-term follow-up studies of children exposed in-utero to modest levels of methylmercury. The failure to detect associations with other neurologic disorders is not surprising as these disorders are not known to be associated with low to moderate doses of methylmercury. Although renal disease has been associated with methylmercury and ethylmercury exposure, it occurs only at a much higher levels of exposure and would not be expected at these exposures.
Premature infants were analyzed separately. After excluding infants who had evidence of neurologic disorders prior to age of first vaccination, there was no evidence of an effect of cumulative mercury exposure. However, we were not given data on the power of the study to detect such effects. If the numbers studied was small, the power may be quite limited. CDC, to its credit, has taken these data seriously and shared them with the public.
They also obtained a second data set from another HMO in the northeast which did not reveal any association with the same disorders; in fact, the new data suggested a possible preventive effect from thimerosal exposure for some of he same outcomes.
No conclusions can be made about causal associations because of the inconsistency in the studies and the nature of the investigations. What is needed is a careful, blinded assessment of children who were exposed to moderate doses of thimerosal as compared to children who received low or no thimerosal from vaccines as was done in the investigations of children exposed in-utero to methylmercury. Hopefully, resources will be committed to such a study as this is the only way to provide definitive data regarding the possible causal association between mercury and these defects.
Blood mercury
levels
Other surprising data included a comparison of blood mercury
levels in a small number of infants who had received thimerosal containing
vaccines vs infants who received vaccines that did not contain
thimerosal. Surprisingly, there was no difference in the blood
mercury concentrations and the levels were only slightly above the lower
limit of detection with the assay (2 mcg/L). However, the details of this
study were not presented. We need to know the exact dose of mercury that
the children received, the age at the time the blood levels were drawn and
the methods of testing. These data appear to be inconsistent with models
predicting blood levels after exposure to thimerosal and the recently
published study of newborns by Stajich et al.
The uncertainties rising from the new data do not resolve any of the controversies or differences of opinion regarding the potential risks from thimerosal in vaccines. Additional studies need to be conducted. IVS believes that a preference should be given for use of vaccines without thimerosal as a preservative wherever possible. Where conditions are such that it is impossible to use only vaccines that do not contain thimerosal as a preservative, the use of no more than one thimerosal-containing vaccine per visit will limit the total exposure to mercury while permitting continued immunization of infants.
updated 06.30.00