Department of Health and Human Services (HHS) Secretary Robert F. Kennedy Jr. has signed off on a Centers for Disease Control and Prevention (CDC) advisory committee recommendation to remove the preservative thimerosal from all flu shots distributed in the U.S.
Thimerosal, which contains mercury, has been used in vaccines for nearly a century to prevent fungal or bacterial contamination after one dose has been drawn from a multidose vial.
In 1999, the HHS, the American Academy of Pediatrics and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure. Two years later, the U.S. recommended that children age 6 and younger not receive vaccines that contain thimerosal.
Anti-vaccine activists have claimed that the preservative can cause autism, though multiple studies, including one by the CDC in 2010, have shown that there is no link.
Last month, RFK Jr.’s revamped Advisory Committee on Immunization Practices (ACIP) recommended against the use of thimerosal in flu shots. In three separate rounds of voting, the ACIP advised that children, pregnant women and adults should not receive vaccines that contain thimerosal. Each of the votes were 5-1 in favor of removing thimerosal from vaccines, with one committee member abstaining.
“After more than two decades of delay, this action fulfills a long-overdue promise to protect our most vulnerable populations from unnecessary mercury exposure,” RFK Jr. said in a release. “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.”
Most companies have already removed the preservative from their vaccines. The exceptions are Sanofi, which produces multidose vials of Fluzone in addition to single-dose syringes, and CSL Seqirus, which includes thimerosal in its multidose vials of Afluria and Flucelvax. Each of these flu shots include a 0.01% concentration of thimerosal.
“We acknowledge the recommendation of the new (ACIP),” a Sanofi spokesperson said in a brief statement. “We will have sufficient supply of Sanofi flu vaccine to support customer preference for this season.”
Meanwhile, a spokesperson from CSL Seqirus said that “delivery of our thimerosal-free flu vaccines for the upcoming season is already underway and we don't expect the ACIP recommendation to have any impact on our vaccine supply or shipment timings."
Both companies have said that they provide many more flu shots in single-dose syringes, which don’t contain thimerosal, than they do in multidose vials.
Last month, during the ACIP meeting, Tracy Beth Hoeg, M.D., Ph.D., of the FDA, told the committee that fewer than 5% of the flu vaccines administered in the 2024-25 season contained thimerosal.
While the decision does not have a major impact on the industry, it does raise concern about the influence of RFK Jr. and his hand-picked panel of ACIP experts, many of whom have expressed anti-vaccine views. Early last month, RFK Jr. dismissed all 17 previous members of the committee.
In placing the lone dissenting vote in the ACIP meeting, Cody Meissner, M.D., of Dartmouth’s Geisel School of Medicine, said the "risk from influenza is so much greater than the nonexistent—as far as we know—risk from thimerosal."
“I would hate for a person not to receive the influenza vaccine because the only available preparation contains thimerosal. I find that very hard to justify,” Meissner added.
Meanwhile, with his decision, RFK Jr. urged "global health authorities to follow this prudent example for the protection of children worldwide."