Thimerosal has been at the heart of Health and Human Services Secretary Robert F. Kennedy Jr.’s antivaccine activism for 20 years. Here’s what to know about the vaccine preservative and its removal from flu vaccines.

The CDC's newly rebuilt Advisory Committee on Immunization Practices (ACIP) took aim Thursday at a mercury-based preservative long targeted by vaccine skeptics, recommending that children, pregnant women, and all other adults use only single-dose seasonal influenza vaccines without thimerosal.

A new slate of vaccine advisers to the US Centers for Disease Control and Prevention voted Thursday to recommend that Americans receive influenza vaccines that are free of thimerosal even though there is no evidence of harm from the preservative.