U.S. Health and Human Services Secretary Robert F. Kennedy Jr. approved a major policy change on Tuesday that will remove the mercury-based preservative thimerosal from all flu vaccines distributed in the U.S.
The decision comes after the CDC's Advisory Committee on Immunization Practices (ACIP) voted 5-1-1 during its June 25-26 meeting to recommend that only single-dose, mercury-free flu shots be given to children under 18, pregnant women, and adults. Kennedy's signature makes that recommendation official federal policy.
Thimerosal is a mercury-containing organic compound (an organomercurial). Since the 1930s, it has been widely used as a preservative in various biological and pharmaceutical products, including many vaccines, to prevent the growth of harmful microbes inadvertently introduced into the vaccine during its use.
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The documented antimicrobial properties of thimerosal contribute to the safe use of vaccines in multi-dose vials, and the ability to package certain vaccines, such as those for seasonal and pandemic influenza, in multi-dose vials.
The ingredient has long been the focus of anti-vaccine campaigns and misinformation. In June, a federal vaccine advisory panel — now including supporters of Robert F. Kennedy Jr.’s views — advised against using the preservative, as highlighted in a Guardian report.
Thimerosal, which contains ethylmercury, has been used safely for decades, with no evidence that it causes harm. In the U.S., it was found in only about 5% of adult flu vaccines, mainly to prevent contamination in multi-dose vials.
"After more than two decades of delay, this action fulfills a long-overdue promise to protect our most vulnerable populations from unnecessary mercury exposure," Kennedy said. "Injecting any amount of mercury into children when safe, mercury-free alternatives exist defies common sense and public health responsibility. Today, we put safety first."
This move is part of a long-standing effort that began in 1999, when the U.S. Public Health Service, the American Academy of Pediatrics, and vaccine makers agreed that mercury should be removed from vaccines due to potential health concerns. While mercury had already been removed from most childhood vaccines, this marks the final step—its removal from all flu vaccines.
The newly appointed members of ACIP, selected under Kennedy's leadership, broke from past committee inaction and pushed forward the full elimination of mercury in flu vaccines, bringing U.S. policy in line with Europe, which phased out mercury in vaccines years ago.
Vaccine manufacturers have stated that they are prepared to transition from multi-dose vials containing mercury to single-dose alternatives, without compromising the vaccine supply for children and adults.
Kennedy has already approved all of the recommendations from the committee's April meeting. Other proposals from the June meeting are still under review.
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