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Vaccine Components

Thimerosal in Influenza Vaccines

Updated: 12/07/2005

Although thimerosal—a mercury-containing preservative—continues to be safely used as a preservative throughout the world (1), in 1999 policy makers in the United States decided to reduce the exposure of infants less than 6 months of age to all forms of mercury, recommending that thimerosal in vaccines to be given to infants under 6 months of age be reduced to only trace amounts or be eliminated altogether. (See Mercury in Vaccines)

All vaccines recommended for universal immunization of infants less than 6 months of age are now manufactured without thimerosal as a preservative. Some vaccines may contain trace amounts of thimerosal from the manufacturing process. (2)

Trivalent inactivated influenza vaccine (TIV) has been recommended for all children 6-23 months of age, in addition to the long-standing recommendations to give TIV to children and adults with certain medical conditions as well as older adults. (3)

Thimerosal-free TIV is not available in the United States. However, TIV is available both with trace amounts of thimerosal and with thimerosal as a preservative. Without thimerosal as a preservative, the vaccine cannot be packaged in multiple dose vials, making delivery of vaccine to large numbers of people—as is often done with TIV—more difficult and making the vaccine more expensive. Packaging vaccine in single dose containers also takes more vaccine and thus may reduce the availability of vaccine for others.

Public health authorities have not expressed a preference for which formulation healthcare providers should use because:

  • there continues to be no scientific evidence that thimerosal as a preservative is harmful
  • the amount of mercury contained in TIV with preservative is within the range that is considered safe
  • TIV is not recommended for children less than 6 months of age.

Parents who would prefer that their child receive TIV without preservative can choose to have their child receive the vaccine that contains only trace amounts.

However, the amount of thimerosal in current inactivated influenza vaccines is so low that it should not raise concern. The issues in 1999 regarding thimerosal in childhood vaccines was for infants in the first 6 months of life and reflected uncertainty about the possible cumulative total ethyl mercury burden from all the thimerosal-containing products administered at newborn, 2, 4 and 6 months of age.

Legislation to prohibit use of TIV containing thimerosal as preservative for children could compromise the availability of TIV for those age groups particularly during time of vaccine shortage. In addition, because of the cost differences, this could create disparities between insured and underinsured children. 

The demonstrated benefits of influenza immunization far outweigh any theoretical risk from thimerosal exposure associated with full implementation of current US influenza vaccine recommendations. (3


1. WHO (2003). Statement on thiomersal from the Global Advisory Committee on Vaccine Safety (GACVS)

2. FDA (2004). Thimerosal Content in Currently Manufactured U.S. Licensed Vaccines.

3. CDC (2004). Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR May 28, 2004 / 53(RR06);1-40.

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