A key vaccine policy advisory group is recommending that the public not receive vaccines that have thimerosal, a mercury-containing preservative that’s used to prevent germs, fungus and bacteria from building up in vials.
While thimerosal isn’t common, the debate over its use at the federal public health level is seen as emblematic of the concerns of health experts, who fear that policies under Health and Human Services Secretary Robert F. Kennedy Jr. will chip away at evidence-based science.
The Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices, comprised of entirely new members appointed by Kennedy, voted Thursday to make the recommendation. The topic appearing on the meeting agenda at all came as a surprise to many in public health and clinician communities. The CDC itself says it’s been long established that there is no evidence that the amount of thimerosal included in some flu vaccines is harmful.
Thimerosal is used in multidose flu vaccine vials to prevent contamination when the second dose is pulled, according to the Food and Drug Administration. The amount of mercury in vials is about equal to the amount of mercury contained in a three-ounce can of tuna, the FDA says.
Vaccine skeptics have promoted the idea that it’s linked to autism and ADHD. Kennedy was editor of a 2014 book titled “Thimerosal: Let the Science Speak,” which called for the removal of the substance from vaccines.
The panel voted 5-1 in three separate votes to recommend single-dose seasonal influenza vaccines that are free of thimerosal for children 18 years and younger, pregnant women and all adults. One member, Vicky Pebsworth, abstained.
The committee also voted 6-0, with Pebsworth abstaining, to reaffirm the panel’s recommendation that people 6 months or older who don’t have “contraindications” receive a routine annual influenza vaccination.
Pensworth said she abstained from the votes because of how the questions were worded and asked for clearer phrasing in the future. She holds doctorates in nursing and public health and also previously served on the FDA vaccine committee as a consumer representative.
Thursday’s meeting, a continuation from Wednesday, was of the first for the panel’s seven new vaccine advisers after Kennedy abruptly fired all 17 former members.
The panel heard a presentation from Lyn Redwood, the former president of the anti-vaccine group Children’s Health Defense, which Kennedy served on as a board member. Redwood said she was giving the presentation in her capacity as a private citizen.
The advisers on the whole were swayed by Redwood’s arguments that thimerosal be removed from vaccines, citing concerns that any kind of mercury exposure could be harmful and it should be minimized over the course of a person’s life.
“If we care about public health we should try to minimize exposure to mercury,” said Martin Kulldorff, the committee’s chair.
If the agency adopts the recommendation, though, the effect may be limited.
Only about 4 percent to 5 percent of the flu vaccines given during the 2024-25 season contained thimerosal, said Tracy Beth Høeg, the FDA liaison on the meeting. Changing the recommendation wouldn’t likely have an impact on availability, she said.
And concerns about thimerosal has been voiced beyond anti-vaccine circles. A 1999 review of mercury in food and drugs, for example, led the CDC to recommend that it not be included in childhood vaccines as a “precautionary measure” to reduce the total amount of mercury that children are exposed to, according to the FDA’s thimerosal information page. All vaccines on the childhood schedule are available in doses that don’t include mercury, the FDA’s webpage states.
Still, the item shouldn’t have even appeared on the agenda, according to panel member Cody Meissner, who returned after having previously served on ACIP. He said that there is no evidence that thimerosal in vaccines is harmful and noted that it’s been used in them since before World War II.
Meissner noted that other countries look to this panel to inform their own policies and that multidose flu vaccine vials are more common in other countries because they’re more affordable than single dose vials. He voted against recommending thimerosal be removed.
He emphasized that it contains ethylmercury, which is excreted more quickly from the body than methylmercury, which is the type found in certain types of fish.
Redwood countered that while mercury leaves the bloodstream quickly, it could build up over time in the brain.
At the meeting, Redwood never explicitly said that there’s a link between thimerosal and autism or ADHD, which has been the claim of skeptics over the years, including from Children’s Health Defense.
Liaison representatives, who sit in on meetings to represent interests of clinicians, pharmacists, and the industry, heavily pushed back on the discussion, asking the panel to reconsider. Kelly Goode, representing the American Pharmacists Association, asked for a more comprehensive presentation from the CDC before the committee takes a vote, which is customary.
Kulldorff responded: “I think it’s inappropriate to dismiss a presentation just because the person does not have a PhD or an M.D.”
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