Thimerosal is a mercury-containing preservative that has been used since the 1930s to prevent contamination of vials that contain more than one dose of vaccine (multi-dose).
|Multi-dose vial of flu vaccine|
The tops of vials are disinfected with alcohol before each use, but alcohol cannot kill all of the microorganisms that might be present, so bacteria or fungi can be introduced into the vial when the stopper is punctured with a needle. Since vaccines contain proteins and other nutrients, bacteria and fungi can multiply inside the vial. Thimerosal kills microorganisms and prevents potentially fatal vaccine reactions.
Because the stopper is punctured only once, single-dose vials do not contain thimerosal. Prefilled syringes of flu vaccine and live attenuated influenza vaccine (LAIV) also do not contain thimerosal.
Other than localized reactions to thimerosal (pain/redness/swelling at the injection site) and rare allergic reactions, no harmful effects from the amount of thimerosal in vaccines has ever been demonstrated. However, in response to public concerns over mercury exposure, the U.S. Public Health Service and American Academy of Pediatrics issued a joint statement in 1999 recommending the removal of thimerosal from all vaccines routinely administered to children (CDC, 1999; Finn & Egan, 2008).
In the United States, all vaccines routinely administered to children do not contain thimerosal or contain only a trace amount of thimerosal. Influenza vaccine is the single exception to that rule. Influenza vaccine formulations in multi-dose vials contain thimerosal, but single-dose vials and prefilled syringes of trivalent inactivated influenza vaccine (TIV; the “flu shot”) do not contain thimerosal. Live attenuated influenza vaccine (LAIV; “nasal spray” flu vaccine) does not contain thimerosal.
Neither CDC’s Advisory Committee on Immunization Practices nor the American College of Obstetricians and Gynecologists express a preference for thimerosal-free influenza vaccines for pregnant women (ACOG, 2010; CDC, 2010). Nevertheless, thimerosal-free influenza vaccines are available for adults and children.
Everything you need to know about thimerosal:
Thimerosal in vaccines is a contentious issue. I’ve included links to information on thimerosal below.
These are my take-home messages:
· All routine childhood immunizations are thimerosal-free or contain only a trace amount of thimerosal.
· Influenza vaccines are available in thimerosal free formulations.
· Some states, including Washington, Oregon, and California have laws restricting the use of thimerosal-containing vaccines.
Thimerosal content of vaccines:
More information on thimerosal:
· Centers for Disease Control and Prevention (CDC): Thimerosal
· Children’s Hospital of Philadelphia: Hot topics: thimerosal
· Food and Drug Administration (FDA): Thimerosal in vaccines
· National Network for Immunization Information: Thimerosal-mercury
American College of Obstetricians and Gynecologists. (2010). Influenza vaccination during pregnancy. Committee Opinion No. 468. Obstetrics & Gynecology, 116(4), 1006-1007. http://www.acog.org/Resources_And_Publications/Committee_Opinions/Committee_on_Obstetric_Practice/Influenza_Vaccination_During_Pregnancy.aspx.
Centers for Disease Control and Prevention. (1999). Recommendations regarding the use of vaccines that contain thimerosal as a preservative. Morbidity and Mortality Weekly Report, 48(43), 996-998. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4843a4.htm.
Centers for Disease Control and Prevention. (1999). Thimerosal in vaccines: a joint statement of the American Academy of Pediatrics and the Public Health Service. Morbidity and Mortality Weekly Report, 48(26), 563-565. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4826a3.htm.
Centers for Disease Control and Prevention. (2010). Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices. Morbidity and Mortality Weekly Report, 59(8). http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5908a1.htm.
Finn, T. M. & Egan, W. (2008). Vaccine additives and manufacturing residuals in United States-licensed vaccines. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (5th Ed.). [Electronic version].