by Sandra Douglas

Created on: October 13, 2010

Thimerosal has been used in vaccines since the 1930’s as a preservative. Its function is to prevent the growth of bacteria in multi-use vials of vaccine. Recent concerns regarding the safety of thimerosal has prompted many consumers to seek thimerosal-free vaccines, and many more wonder if the concerns are valid.

Thimerosal contains 49% ethylmercury. Some studies have linked thimerosal and mercury to a rise in the rates of autism in the United States in recent years, though the Center for Disease Control (CDC) has dismissed the claims.

The low dose of thimerosal that is present in the vaccines is considered safe by the Food and Drug Administration (FDA) but just the same, vaccine manufacturers agreed to reduce or eliminate thimerosal from common pediatric vaccines as a precaution. Currently, most vaccines manufactured in the U.S. do not contain thimerosal or contain only trace amounts.

The exception to this is the influenza vaccines. In 2009, a separate flu vaccine was required to protect against the H1N1 flu virus, also known as Swine flu. Some positive news is that, beginning in 2010, the seasonal flu vaccine includes protection against the H1N1 virus, along with the A-H2N3 virus, and B virus. Two different flu vaccines will no longer be necessary.

Some parents are concerned enough about the risk of thimerosal side effects that they seek thimerosal free vaccines. Preservative-free and thimerosal free vaccines are available, but so far, quantities are limited. This situation will improve over time as manufacturing capabilities are increased along with consumer demand for the product.

For the 2010-2011 flu season, manufacturers expect to produce 160-165 million doses of flu vaccine. 74 million doses of thimerosal free or preservative-free (trace) will be available.

Most of the flu vaccine manufactured in the U.S. contains thimerosal but in some vaccines the amount is so small that the FDA considers it to be thimerosal free. The thimerosal is used early in the manufacturing process and by the time the vaccine is complete, the thimerosal is so diluted that it no longer acts as a preservative and so the vaccine is considered preservative-free.

Preservatives are important in multi-dose vials of vaccine. Vials are stored in the refrigerator of a doctor’s office or clinic and when a dose of flu shot is needed, the vial is accessed using a new sterile needle and syringe. Preservatives prevent the growth of bacteria in case of accidental contamination of the vial. Single use vials do not require preservative.

One of the concerns of thimerosal in vaccines is the presence of mercury. The amount of mercury is small and considered safe. However, the amount varies between manufacturers. If you are concerned about the presence of thimerosal and mercury in your vaccines, a table of detailed information by manufacturer is available for the 2010-2011 flu season at http://www.cdc.gov/flu/about/qa/vaxsupply.htm. Visit the website then discuss your concerns and options with your health care provider.

Reference:

www.cdc.gov/flu

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