Infographic: What Goes Into a Vaccine? Thimerosal Spotlight

Today's vaccines use only the ingredients needed so they work and are safe.

Spotlight on Thimerosal: pronounced tie-mur-us-sl

What is Thimerosal?

Thimerosal is an ethylmercury-based preservative. Unlike methylmercury—the kind of mercury that’s found in some fish—ethylmercury leaves our bodies quickly and easily.

Why is thimerosal used?

Thimerosal is used in small amounts. It is only added into the storage tubes that hold many doses of flu vaccine.

Small amounts are used.

Thimerosal is used to stop germs from growing in the vaccine storage tube when a health care provider is drawing a dose from the tube.

Is it safe to use?

Thimerosal has been proven to be safe. People sometimes have minor side effects, like redness and swelling in their arms where the vaccine was given. Serious allergic reactions to thimerosal are rare.

Safety Checks

Before they are approved for use in the United States, vaccines are tested to make sure they work, and are safe. After approval, the CDC and the FDA keep tracking the vaccine’s safety.

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This resource is supported by the Centers for Disease Control and Prevention of the U.S. Department of Health and Human Services (HHS) as part of a Cooperative Agreement. The contents are those of the author(s) and do not necessarily represent the official views of, nor an endorsement, by CDC/HHS, or the U.S. Government.

Download the Infographic

This iREACH infographic provides information on ingredients that are used in vaccines, specifically highlighting thimerosal.

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