A federal vaccine advisory panel, overhauled by Health Secretary Robert F. Kennedy Jr., has recommended against the use of seasonal influenza vaccines containing the preservative thimerosal, a decision that could ripple through global vaccine supply chains and reshape future flu campaigns in the United States.
The move marks another milestone in Kennedy’s long-running crusade against certain vaccine ingredients, despite a broad scientific consensus that thimerosal poses no harm. The Advisory Committee on Immunization Practices (ACIP), which operates under the Centers for Disease Control and Prevention, voted to restrict the use of thimerosal-containing flu vaccines across all age groups. The final tally was five in favor, one abstention, and one opposed.
That lone dissent came from Dr. Cody Meissner, a pediatrician and professor at the Geisel School of Medicine at Dartmouth, who warned the move could have unintended consequences. “The risk from influenza is far greater than the nonexistent—as far as we know—risk from thimerosal,” Meissner said. “I would hate for someone to forgo the flu vaccine just because the only available formulation contains thimerosal — I find it very hard to justify.”
The ACIP plays a critical role in shaping national immunization practices, issuing guidance that informs both physicians and insurance providers on which vaccines to administer.
In June, Kennedy abruptly dismissed all 17 previous committee members, citing alleged conflicts of interest, and replaced them with eight new appointees, all aligned with his skepticism of mainstream vaccine policies.
Originally set to focus on routine recommendations for COVID-19 and HPV vaccines, the panel added the thimerosal issue to the agenda at the last minute. While reaffirming its recommendation that all Americans over six months of age receive a flu shot, the committee specified that it should be free of the controversial preservative.
Thimerosal has long been a lightning rod in vaccine debates, despite decades of research finding no evidence of harm. Many medical associations urged the committee not to endorse the restriction. “There’s a big difference between what was said in the meeting and reality,” said Dr. Sean O’Leary, chair of the Committee on Infectious Diseases at the American Academy of Pediatrics. “The science on thimerosal is settled, and the rhetoric used to suggest otherwise is misleading and harmful.”
Thimerosal, an ethylmercury-based preservative, has been used in vaccines since before World War II. Today, it is present in roughly 5% of seasonal flu vaccines sold in multi-dose vials, which are cheaper and easier to store than single-dose alternatives.
Scientific data show that ethylmercury — unlike its cousin methylmercury, found in seafood — is quickly eliminated from the body. Its half-life in the blood is about seven days, compared to 44 to 58 days for methylmercury. A single flu shot contains about 25 micrograms of ethylmercury — less than what’s found in a 3-ounce can of tuna, which typically has about 40 micrograms of methylmercury.
Thimerosal was removed from most pediatric and many adult vaccines in the early 2000s as a precaution, a move some experts criticized as potentially fueling unwarranted public fears. Subsequent large-scale studies conducted in multiple countries found no link between the preservative and neurological disorders, and most of the medical establishment has long considered the issue closed.
Nonetheless, the committee on Thursday, June 26, skipped a scheduled CDC presentation that included much of this data. Instead, members heard from Lyn Redwood, a nurse and founder of the World Mercury Project — the predecessor to Kennedy’s current anti-vaccine organization, Children’s Health Defense.
