for Japanese Encephalitis
What is mercury and what is thimerosal?1 Mercury is a naturally occurring element found in the earth's crust, air, soil and water. Mercury has been released into the environment through volcanic eruptions, weathering of rocks and burning of coal. Once released, certain types of bacteria in the environment can change mercury to methylmercury. Methylmercury makes its way through the food chain in fish, animals, and humans. At high levels, it can be toxic to people.
Thimerosal, a preservative still used in some vaccines, is a mercury-containing organic compound which has a different form of mercury called ethylmercury. Studies comparing ethylmercury and methylmercury suggest that they are processed differently in the human body. Ethylmercury is broken down and excreted much more rapidly than methylmercury. It appears that ethylmercury (the type of mercury in the influenza vaccine) is removed from the body more quickly than methylmercury (the type of mercury in the environment).
What are Washington's legal limits on mercury in vaccines? As of July 1, 2007, Washington state law requires that pregnant women and children under three years of age be given vaccines that have no more than 0.5 micrograms of mercury per 0.5 milliliter dose. The law makes an exception for mercury content of influenza vaccine and allows pregnant women and children under age three to get influenza vaccine if it has 1.0 microgram of mercury per 0.5 milliliter dose, or less. Your doctor or nurse can help explain the size of these amounts.
Can the legal limit on mercury in vaccines be suspended? Washington state law allows the secretary of the Washington department of health to suspend the state's legal mercury limit for a vaccine if the secretary determines there is a shortage of vaccine available to protect the public health against vaccine-preventable disease.
How does this apply to me? Once Washington's legal mercury limit for a vaccine has been suspended, state law requires the following people be informed they are being given a vaccine containing mercury level exceeding those limits:
|•||Women known to be pregnant or lactating.|
|•||The parent or legal guardian of a child under eighteen years of age receiving the vaccine.|
1Information about mercury, methylmercury thimerosal and ethylmercury stated in the answer to this question was taken from the following two sources: Children's Hospital of Philadelphia at http://www.chop.edu/consumer/index.jsp and the Food and Drug Administration at www.fda.gov/cber/vaccine/thimerosal.htm.