The Advisory Committee on Immunization Practices (ACIP), restructured under Robert F. Kennedy Jr., has issued a recommendation advising against the use of flu vaccines that contain thimerosal, a preservative used for decades in multidose vials. Although the recommendation impacts only a small portion of the U.S. flu vaccine supply, it marks the committee’s initial action since being reconstituted and reflects a departure from long-standing vaccine practices.
Thimerosal, which contains ethylmercury, is included in multidose flu vaccines to prevent bacterial contamination. Anti-vaccine proponents have alleged a link between thimerosal and autism, though scientific research, including a 2010 CDC study, has found no evidence to support that claim.
Tracy Beth Hoeg, M.D., Ph.D., representing the FDA, informed the committee that fewer than 5% of flu vaccines used during the 2024–25 season included thimerosal.
The ACIP reviewed a presentation from Lyn Redwood, a former president of Children’s Health Defense, who referenced a 2008 study from the University of California, Davis. The study, however, is not available in the public domain, and a researcher named in the study has distanced himself from Redwood’s interpretation.
The revised ACIP, composed of eight members appointed by RFK Jr.—one of whom has since stepped down—voted Thursday afternoon to recommend the use of only single-dose vials of influenza vaccines that do not contain thimerosal. Cody Meissner, M.D., of Dartmouth’s Geisel School of Medicine, was the sole panel member to vote against the measure.
“The risk from influenza is so much greater than the non-existent—as far as we know—risk from thimerosal,” Meissner stated. “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.”
Another member, Vicky Pebsworth, Ph.D., abstained from voting due to concerns about how the voting questions were structured. Pebsworth also remarked that the committee should avoid taking actions that limit vaccine availability, especially for vaccines already approved by the FDA and included in the immunization schedule.
Despite the new stance on thimerosal, the ACIP voted unanimously to continue recommending annual influenza vaccination for individuals aged six months and older.
Robert F. Kennedy Jr., who was recently appointed Secretary of the Department of Health and Human Services, had previously dismissed all 17 members of the original ACIP and replaced them with the new panel. This development has led to criticism from various public health stakeholders.
Following the vote, the Partnership to Fight Infectious Disease issued a statement urging Kennedy to reinstate the former ACIP membership and enhance FDA participation in the committee’s processes.
In response to the ACIP’s decision, Dr. Katherine O’Brien of the World Health Organization addressed the preservative’s safety on Friday, stating, “Thimerosal has been reviewed multiple times by multiple agencies, including WHO, and it’s clear from the evidence that there is no evidence of harm from the use of thimerosal.”
The final implementation of ACIP recommendations typically requires sign-off by the CDC director. However, the position is currently vacant.
