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Vaccine Concerns |
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Thimerosal |
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What is Thimerosal? |
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| "Although
the names may sound the same, methylmercury and ethylmercury are
very different. An analogy is the difference between methyl alcohol
and ethyl alcohol: Methyl alcohol is antifreeze, and ethyl alcohol
is a Bud light." |
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Dr. Ari Brown, pediatrician and author
of popular books for parents about infant and child health and
development. |
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| Food
and Drug Administration |
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| What
is Thimerosal? |
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| Thimerosal is a preservative that has been
used in some vaccines since the 1930's, when it was first introduced
by Eli Lilly Company. It is 49.6% mercury by weight and is metabolized
or degraded into ethylmercury and thiosalicylate. Prior to its introduction
in the 1930's, data were available in several animal species and humans
providing evidence for its safety and effectiveness as a preservative.
Since then, thimerosal has a long record of safe and effective use
preventing bacterial and fungal contamination of vaccines, with no
ill effects established other than minor local reactions at the site
of injection. Although it was not used in all vaccines (for example,
it has never been used in live virus vaccines such as MMR or chickenpox
vaccines), it had been part of the manufacture of many vaccines in
use in the United States and other countries until recently. |
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| As a vaccine preservative, thimerosal is
used in concentrations of 0.003% to 0.01%. A vaccine containing 0.01%
thimerosal as a preservative contains 50 micrograms of thimerosal per
0.5 ml dose or approximately 25 micrograms of mercury per 0.5 mL dose.
The use of mercury-containing preservatives in vaccines has declined
markedly since 1999 (to view recommendation, visit
MMWR's website). Thimerosal has been removed from or reduced to
trace amounts in all vaccines routinely recommended for children 6
years of age and younger, with the exception of inactivated influenza
vaccine. A preservative-free version of the inactivated influenza vaccine
(contains trace amounts of thimerosal) is available in limited supply
at this time for use in infants, children and pregnant women. Some
vaccines such as Td, which is indicated for older children (≥ 7
years of age) and adults, are also now available in formulations that
are free of thimerosal or contain only trace amounts. Vaccines with
trace amounts of thimerosal contain 1 microgram or less of mercury
per dose. |
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| This
page was reviewed on
February 25, 2011 |
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Immunization Action Coalition • 1573 Selby Ave • St. Paul, MN 55104 |
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tel 651-647-9009 • fax 651-647-9131 |
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This website is supported in part by a cooperative agreement from the National Center for Immunization and Respiratory Diseases (Grant No. 5U38IP000290) at the Centers for Disease Control and Prevention (CDC) in Atlanta, GA. The website content is the sole responsibility of IAC and does not necessarily represent the official views of CDC. |
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