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HHS approves thimerosal removal from flu vaccines

HHS Secretary Robert F. Kennedy Jr. backs the removal of thimerosal from U.S. flu vaccines following a CDC advisory committee vote, impacting less than 5% of shots.

Alivia Kaylor, MSc
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Published: 24 Jul 2025

Yesterday, Health and Human Services Secretary Robert F. Kennedy Jr. adopted an Advisory Committee on Immunization Practices recommendation to remove thimerosal from the limited number of influenza vaccines that still contain the preservative. This move will affect multi-dose formulations, which account for less than 5% of all flu vaccines.

The decision follows a 5-1 vote made last month by the CDC's newly restructured advisory committee, now composed of Kennedy's hand-selected appointees, to eliminate thimerosal from flu vaccines for children, pregnant individuals and adults.

The removal is likely to hit developing countries the hardest -- where multi-dose vials are commonly used due to their cost and distribution advantages.

Use of thimerosal in vaccines

Since the 1930s, thimerosal has been used in vials made for multiple administrations to prevent microbial contamination. The mercury-derived preservative is metabolized into ethylmercury, a compound different than the neurotoxic methylmercury that bioaccumulates in seafood. 

Despite its well-studied safety at low levels, thimerosal has long been targeted by the anti-vaccine crowd. In 1999, the CDC and medical societies recommended its removal from pediatric vaccines. By 2001, it was eliminated from all routine childhood immunizations.

Today, only three flu vaccines administered in the U.S contain thimerosal (0.01%), including the multi-dose formulations of Sanofi's Fluzone and Seqirus' Alfluria and Flucelvax.

HHS noted in the announcement that manufacturers have confirmed they can fully replace these multi-dose formats with preservative-free alternatives.

ACIP review

With the CDC director position currently unfilled, Kennedy finalized the recommendation himself. In a statement, HHS called the move part of a broader effort to "restore trust with Americans by removing risk while sustaining access to vaccines."

The ACIP meeting also featured a presentation by known vaccine skeptic, Lyn Redwood of Children's Health Defense, which cited animal and in vitro studies often used to question thimerosal's safety. One cited study was later removed after it was reported to not exist.

While ACIP also unanimously reaffirmed its recommendation for annual flu vaccination for individuals six months and older, Kennedy has not yet approved that guidance. HHS says additional recommendations from the June meeting remain under review.

Alivia Kaylor is a scientist and the senior site editor of Pharma Life Sciences.

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