Question: I’ve heard that the swine flu vaccine contains thimerosal, a preservative that has mercury in it. Is that true, and can it cause autism and other health problems?
Answer: It’s true that some formulations of the swine (H1N1) and seasonal flu vaccines contain thimerosal. Numerous studies have found no association between the mercury-containing preservative and autism or other health problems. Nevertheless, thimerosal has been the subject of much controversy and, unfortunately, much misinformation.
Since the 1930s thimerosal has been used in vaccines to prevent dangerous bacterial or fungal contamination,which can occur, for example, inside multi-dose vaccine vials. The preservative became a concern in the late 1990’s. That’s when research by the FDA showed that the cumulative amount of mercury an infant received from vaccines over his or her first 6 months of life could be more than the EPA’s recommended limit for methylmercury. The type of mercury used in vaccines, called ethyl mercury, has been found to be less toxic in humans than the methyl mercury you get from environmental sources (eating certain fish, for example). Methyl mercury is so dangerous because it’s difficult for the body to purge, meaning it’s more likely to build up in your system over time than ethyl mercury.
As a precaution, in 1999 health officials recommended that vaccines typically administered in early childhood should have their thimerosal content reduced or eliminated. Manufacturers responded. Since 2001, all vaccines recommended for children 6 and under have been produced with either no thimerosal or only trace amounts, with the exception of some versions of the flu shot. Newer studies have overwhelmingly found that the amount of thimerosal used in the childhood vaccines before 2001 did not cause neurological damage. Today, influenza vaccines are the only ones given to young children that may contain more than trace amounts of thimerosal as a preservative.
Neal Halsey, M.D., a former member of the committee that recommended that thimerosal be reduced or removed from vaccines administered to young infants as quickly as possible back in 1999, notes that “the removal of thimerosal from influenza vaccines has taken much longer than for other vaccines because of the need to produce them in eggs, which has a potential for contamination during the production process, and the need to use multi-dose vials for production of pandemic vaccines.” Halsey, who is director of the Institute for Vaccine Safety in the Department of International Health at Johns Hopkins Bloomberg School of Public Health, says he has “no concerns about thimerosal in influenza vaccines,” and strongly supports the vaccine programs for both the seasonal and H1N1 flus.
If you want to reduce your or your children’s overall exposure to mercury, manufacturers do offer H1N1and seasonal flu vaccines that contain no thimerosal. They include:
- The single dose flu shots produced by CSL Limited and Sanofi Pasteur
- The intranasal vaccines produced by MedImmune
- The Novartis single-dose H1N1 flu vaccine has just trace amounts of mercury
While the evidence on thimerosal ultimately turned out to be reassuring, the controversy has had an unfortunate result: a profound distrust among some Americans in a vaccine program that’s effective in preventing disease. We’re glad that consumers now have the option of a mercury-free flu vaccine. But even if you can’t find a thimerosal-free version, it’s probably unwise to skip the flu vaccine altogether. While the risks from thimerosal, if any, are theoretical, the dangers from influenza—particularly to young children and pregnant women—are very real. That’s especially true for this year’s swine flu.
You can find out more about which vaccines contain thimerosal and which don't at the Institute for Vaccine Safety's website maintained by Johns Hopkins Bloomberg School of Public Health. For more on the purported autism/vaccine link, see To Vaccinate or Not To Vaccinate?
--Kevin McCarthy, associate editor