Institute for Vaccine Safety 



There are numerous factors associated with mercury toxicity, as noted on the slide. All children are not created equal with regard to their risk from exposure to mercury. We cannot control many of these factors, but we can have some control over the age and weight of children at the time they are exposed to mercury in vaccines






Exposure to a fixed dose (e.g. 62.5 ug) of mercury at 2 months of age poses a greater potential risk than the same dose administered at 6 months of age because a child weighs more at 6 months and the target organ, the brain, is more vulnerable early in life.

Similarly, exposures at 9-12 months would carry much less theoretical risk than exposure to the same dose at 2 months of age.

The recent American Academy of Pediatrics/ Public Health Service recommendation to defer the first dose of hepatitis B vaccine for infants born to HBsAg negative mothers until 2-6 months of age has addressed the problem of exposure at birth, but the exposure to mercury at 2 months of age is much greater and we need to do more to reduce this potential exposure.








This figure shows the ATSDR guidelines selected by the Public Health Service superimposed on the daily exposures to ethyl mercury for children who receive all thimerosal-containing vaccines. At 2 months of age children of all weight categories receive more than 30 times the recommended daily maximum exposure and children of the smallest weight category receive almost three months worth of daily exposures on a single day.

If the EPA or WHO guidelines are used, the smallest children receive approximately 8 months of daily exposures in a single day. None of the guidelines provide us with the safety margin for these exposures or how single large exposures should be counted. Physicians administering vaccines and parents must make a decision at the time of immunization as to the safety of the dose of mercury delivered.





    We need to tell physicians and parents about the options available for reducing mercury exposures. If only a single thimerosal-containing vaccine is administered such as Hib or DTaP at two, four and six months of age, then only the very smallest infants receive more than the total monthly mercury exposure allowed under the ATSDR guidelines.





Slide 17 of 26

    Slide Notes:

    Administering only hepatitis B vaccine gives one-half the mercury exposure and most children receive less than the weekly allowable dose after two months of age.





As noted by Kathryn R. Mahaffey, PhD, the EPA estimates that seven percent of women of childbearing age consume sufficient fish to have a mercury exposure of about 0.1 micrograms per kilogram per day, the upper level that EPA considers to be safe. The EPA also notes that about one percent of women of childbearing age are consuming 0.37 micrograms or more per kilogram of mercury per day, which is more than the ATSDR reference value.

Thus, some children are being born with mercury from their mother’s exposures that are above the guidelines provided by EPA, ATSDR, and WHO. Although safety factors have been built into these guidelines, we do not know what the effects of additional mercury will be on the developing brain.




Throughout the country there are warnings about mercury exposure from fish directed to pregnant women, nursing women, and in some cases for children as noted in this poster from Maine. Local populations, especially Native Americans, often ignore these guidelines.




Thimerosal is not a perfect preservative, as evidenced by numerous clusters of disease caused by DTP vials that had become contaminated with the group A streptococcus

Manufacturers should be encouraged to use unit dosing for vaccine delivery whenever possible. Not only does this preclude the need for preservatives such as thimerosal, but this can eliminate errors from improper reconstitution or mixing of vaccines. Although these errors occur infrequently, they can be harmful. There are drawbacks to unit dosing, including increased refrigerator space requirements, but newer developments may reduce space requirements. There are also increased costs associated with unit dose delivery, which will need to be addressed.



The last point is that we need to have good science used for decision making in the review of alternatives to thimerosal and the effects on the final product from reducing or removing thimerosal from vaccines. We expect scientists at the Food and Drug Administration to help manufacturers address these problems. Instead of increasing the budget to address increasing numbers of safety concerns in the past five years, the budget for research at CBER (Center for Biologics and Related Products) has decreased to one third of what it was in 1994. This trend must be reversed in order to maintain the tradition of good science at the FDA and protect children against disease with the safest possible vaccines.