Vaccine Q&A

Questions and answers about swine flu

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Thursday, October 22, 2009

Andrew Pekosz, an associate professor of molecular microbiology and immunology at Johns Hopkins University's Bloomberg School of Public Health in Baltimore, answers a reader about H1N1 "swine" flu.

What is thimerosal, and why are people upset that it's in vaccines?

Thimerosal is a preservative used in a number of vaccines. It helps keep the vaccine free of contaminating bacteria and fungi. It contains a small amount of mercury, which is what causes people to be concerned about it. The dose of mercury you get from a vaccine containing thimerosal is far below the limits of mercury exposure, but the fact that thimerosal has mercury in it causes many people to be concerned about getting injected with it. It is not associated with any adverse side effects at the doses present in influenza vaccines, but it is being eliminated from childhood vaccines due to public concern.

Does either the injection form or nasal spray form of the H1N1 vaccine contain thimerosal?

The nasal spray vaccine does not contain thimerosal. Some batches of the injected vaccine are thimerosal-free, but some aren't. . . . You should be able to ask about this when you go and get your shot: Thimerosal should be on the label of the vaccine if it's a component.

-- Rachel Saslow

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