• The United States Department of Health and Human Services has said it will officially remove the preservative thimerosal from all flu vaccines distributed in the country.
• Thimerosal is a mercury-based preservative that — due to questions about its safety throughout the decades — has mostly been avoided by vaccine producers.
• However, it still features in some flu shots in the U.S., which has prompted questions about how a ban on thimerosal may affect vaccine availability and accessibility.

Written by Maria Cohut, Ph.D. — Updated on July 24, 2025

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