The Advisory Committee on Immunization Practices (ACIP), recently remade by Health Secretary Robert F. Kennedy Jr., voted Thursday in favor of only recommending flu shots that don’t contain the mercury-based preservative thimerosal.
The ACIP, which provides guidance to the Centers for Disease Control and Prevention (CDC), voted on four draft recommendations, three of which had to do with recommending only single-dose, thimerosal-free flu vaccines for various demographics.
On the question of recommending only thimerosal-free seasonal flu vaccines for children 18 and under, pregnant women and all adults, the committee voted 5-2 in favor of the recommendations with one member voting “No” and another abstaining.
On the question of recommending seasonal flu vaccines for the 2025-2026 flu season for people six months and older, all seven voting members voted “Yes.”
Thimerosal, roughly half of which is composed of ethylmercury, is used in multi-dose vaccine vials to prevent the growth of bacteria and fungi. Anti-vaccine proponents have long argued there is a link between thimerosal and neurological conditions like autism despite multiple epidemiological studies finding no connection.
The CDC’s webpage on thimerosal also states, “Many well conducted studies have concluded that thimerosal in vaccines does not contribute to the development of autism.”
“Even after thimerosal was removed from almost all childhood vaccines, autism rates continued to increase, which is the opposite of what would be expected if thimerosal caused autism,” the CDC notes.
Thimerosal-free vaccines are widely available and are the most commonly administered in the U.S. Vaccines containing thimerosal are more common in low-income countries as multi-dose vials are less expensive.
Cody Meissner, a professor of pediatrics at the Geisel School of Medicine at Dartmouth College who previously served on ACIP, was the sole member to speak out against the recommendation. and vote “No” on the recommendations.
Following a presentation on thimerosal by Lyn Redwood, former head of the anti-vaccine group, Children’s Health Defense, in which she strongly suggested the levels of mercury in thimerosal-containing vaccines was having a detrimental effect on children, Meissner strongly pushed back on the claims.
“One of the most important to remember is that thimerosal is metabolized into ethyl mercury and thiosalicylate. It’s not metabolized into methylmercury, which is in fish and shellfish. Ethylmercury is excreted much more quickly from the body. It is not associated with the high neurotoxicity that methyl mercury is,” Meissner said. “Of all the issues that I think we ACIP needs to focus on, this is not a big issue.”
ACIP member Vicky Pebsworth abstained from voting. In explaining her vote, she said, “My personal views on this is that we should not be doing anything that restricts access to vaccines of any sort, especially those that are already approved by the FDA and that are already in the schedule.”
“My problem, and the reason I abstained for all of these votes, is because of the way the voting question was written. In the world of survey research, you don’t ask two things in the same question,” she added, noting how two questions were conflated into one recommendation, whether vaccines should be recommended and whether they should contain thimerosal.
“Yes, I think we should not be using thimerosal as a preservative, but we didn’t get into any sort of a discussion about the first part of the question.”
