Thimerosal: A Brief Overview
- Thimerosal is a mercury-containing preservative that has been used in medical
products since the 1930s. It is used to help ensure that these products do not
become contaminated by microorganisms.
- Thimerosal is a derivative of ethyl mercury.
- Mercury is a chemical element found in the environment, foods (particularly
seafood), and some household items. Everyone is exposed to mercury during their
lifetime. Federal agencies have developed specific guidelines regarding safe levels
of exposure to mercury and mercury-containing products.
Thimerosal and Vaccines
- Thimerosal is added in small amounts to some vaccines to keep microorganisms from
growing in the vaccine.
- There is no evidence that children have been harmed by the amount of mercury found
in vaccines that contain thimerosal.
- In a review of pediatric vaccines in 1999, the Food and Drug Administration (FDA)
found that mercury exposure from vaccines containing thimerosal was within the
safety margins established by the FDA, the Agency for Toxic Substances and Disease
Registry (ATSDR), and the World Health Organization (WHO) for methyl mercury, a
closely related organomercurial. The maximum amount of ethyl mercury from thimerosal
in vaccines could have exceeded the Environmental Protection Agency (EPA) guidelines
that were established for methyl mercury, depending on the vaccine formulations
received. It should be recognized that EPA guidelines were meant to be protective of
the developing fetus; therefore, it is likely that EPA guidelines provide an even
greater margin of safety for infants and small children. The use of thimerosal in
pediatric vaccines has decreased markedly since August 1999 (see below).
- Parents should consult their child�s health care provider before vaccination if
they believe the child may be allergic or sensitive to products that contain
thimerosal.
Making Safe Vaccines Even Safer
- The Federal Government is working closely with vaccine companies to eliminate or
reduce mercury in any products currently available on the market.
- In August 1999, the FDA approved a thimerosal-free hepatitis B vaccine
manufactured by Merck and Co., and in March 2000, approved a thimerosal-reduced
(less than 0.5 micrograms of mercury per dose) hepatitis B vaccine manufactured by
Glaxo SmithKline. In March 2001, the FDA approved a newly formulated version of
Aventis Pasteur�s Tripedia, a diphtheria, tetanus, and acellular pertussis (DTaP)
vaccine containing only a trace of thimerosal (less than 0.5 micrograms of mercury
per dose.) Additionally, Wyeth-Lederle Vaccines and Pediatrics now market only a single-dose, thimerosal-free formulation of
its Haemophilus influenzae type b (Hib) vaccine in the United States.
- With the recent approval of the reformulated Tripedia, all routinely recommended
pediatric vaccines will be available as either completely thimerosal-free or contain
only trace amounts of thimerosal. The routinely recommended pediatric vaccines are:
hepatitis B; Haemophilus influenzae type b (Hib); pneumococcal conjugate
vaccine; DTaP; inactivated polio vaccine; mumps/measles/rubella (MMR) vaccine; and
the varicella (chickenpox) vaccine.
- The Centers for Disease Control and Prevention (CDC), the FDA, the National
Institutes of Health (NIH), and other Federal agencies routinely monitor and conduct
research to examine any new evidence that would suggest possible problems with the
safety of vaccines.
CDC, National Immunization Program: http://www.cdc.gov/nip
Last updated: September 2001
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