Thimerosal
Thimerosal is a very effective preservative that has
been used since the 1930s to prevent contamination in some
multi-dose vials of vaccines (preservatives are not required for
vaccines in single-dose vials).
Thimerosal contains approximately 49% ethyl mercury.
There is no convincing evidence of harm caused by the low doses of
thimerosal in vaccines, except for minor reactions like redness and
swelling at the injection site.
However, in July 1999, the Public Health Service
(PHS) agencies, the American Academy of Pediatrics (AAP), and
vaccine manufacturers agreed that thimerosal should be reduced or
eliminated in vaccines as a precautionary measure.
Today,
with the exception of some flu vaccines,
none of the vaccines used in the U.S. to protect preschool
children against 12 infectious diseases contain thimerosal as a
preservative.
Why is thimerosal still in flu vaccine?
The removal of thimerosal as a preservative from
influenza vaccine is a complicated process. The total amount of flu
vaccine without thimerosal as a preservative will be increased as
vaccine manufacturing capabilities are expanded.
In the meantime, it is important to keep in mind
that the benefits of influenza vaccination outweigh the theoretical
risk, if any, for exposure to thimerosal. Each year, an average of
about 36,000 people in the United States die from influenza, and
114,000 are admitted to the hospital as a result of influenza.
People age 65 years and older, people of any age with chronic
medical conditions, and very young children are more likely to have
complications from influenza than from thimerosal in the vaccine.
Children's Safety
With the newly formulated childhood vaccines, the
maximum total exposure during the first six months of life is now
less than three micrograms of mercury. Based on guidelines
established by the Food and Drug Administration (FDA), the Environmental Protection Agency (EPA),
and the Agency for Toxic Substances and Disease Registry (ATSDR), no
child will receive excessive mercury from childhood vaccines
regardless of whether or not their flu shot contains thimerosal as a
preservative.
The risks of severe illness from influenza infection are elevated
among young children. In 2003 12 Colorado children died from
influenza. The benefits of influenza vaccination outweigh the
theoretical risk, if any, of thimerosal exposure through
vaccination.
Women's Reproductive Safety
A study of influenza vaccination examining over
2,000 pregnant women demonstrated no adverse fetal effects
associated with influenza vaccine. Case reports and limited studies
indicate that pregnancy can increase the risk for serious medical
complications of influenza. One study found that out of every 10,000
women in their third trimester of pregnancy during an average flu
season, 25 will be hospitalized for flu-related complications.
Additionally, influenza-associated excess deaths among pregnant
women have been documented during influenza pandemics. Because
pregnant women are at increased risk for influenza-related
complications and because a substantial safety margin has been
incorporated into the health guidance values for organic mercury
exposure, the benefits of influenza vaccine with reduced or standard
thimerosal content outweighs the theoretical risk, if any, of
thimerosal.
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