What is thimerosal?
Thimerosal is a preservative found in many vaccines as well as other drug products, widely used since the 1930s. Preservatives are necessary to prevent growth of bacteria or fungi in the vaccine. This is especially important in multi-dose vials. Because preservatives will not eliminate absolute risk of contamination, nurses should practice safe hygiene when drawing up the vaccine. Thimerosal is a mercury-containing organic compound that is 49% mercury by weight.

Is Thimerosal safe?
Yes. There has been no convincing evidence of harm directly linked to thimerosal, although mercury-containing products do have a potential for affecting the nerve system. The FDA and the EPA are actively involved in research to better understand any possible health effects of thimerosal and continue to monitor its use. The FDA recommends a thimerosal-free or thimerosal-reduced flu vaccine for pregnant women.

What is an allergic response?
An allergic response to thimerosal is usually mild and can be identified by redness and/or swelling of the injection site.

The forecast...
Public Health Service Agencies, along with vaccine manufacturers, agree that the use of thimerosal should be reduced or eliminated as a precautionary measure. Thimerosal has been successfully removed or reduced to trace amounts in all vaccines for children 6 years of age and younger, with the exception of inactivated influenza.

Today, all routinely recommended pediatric vaccines are manufactured with only trace amounts or no thimerosal, with the exception of influenza vaccines. Thimerosal-free vaccines are available but in limited quantities. As the ability of manufacturing Thimerosal-free vaccines increases, availability will also increase.

Additional resources

Centers for Disease Control and Prevention

U.S. Food and Drug Administration