By Josh Nathan-Kazis

The debut meeting of Robert F. Kennedy Jr.'s handpicked vaccine committee has made clear that vaccine skeptics, once a fringe movement in U.S. politics and culture, have taken control of a key mechanism for U.S. vaccine regulation.

In a series of votes on Thursday, all of which were five to one in favor with one abstention, the CDC's Advisory Committee on Immunization Practices (ACIP) recommended against any use of flu vaccines that contain a preservative known as thimerosal. The ingredient has long been a focus of antivaccine advocates.

The vote was largely symbolic. Thimerosal is used in a tiny minority of the flu shots administered in the U.S. today. Both the Food and Drug Administration and Centers for Disease Control and Prevention have said that there is no evidence to support a link between thimerosal and autism, a longstanding concern.

Antivaccine groups have continued to argue that thimerosal poses a health threat. On Thursday, they appeared to win a policy change, enabled by Kennedy's new appointees, that conforms with their longstanding arguments against thimerosal.

The vote came after a presentation by the former president of Children's Health Defense, the antivaccine group that Kennedy founded. In the ensuing discussion, the lone dissenting voice came from Dr. Cody Meissner, who served on ACIP years ago and was recently added back after Kennedy fired the entirety of the committee earlier this month and appointed new members.

"I'm not quite sure how to respond to this presentation," Meissner began. "Of all the issues that I think ACIP needs to focus on, this is not a big issue."

The ACIP debate over thimerosal, once a worry of antivaccine groups, signals the changes that Kennedy has already brought to U.S. vaccine policy. During the meeting's opening session Wednesday, the new chair said that the committee and its subsidiary workgroups would be reconsidering much of the vaccine playbook that U.S. health officials have used for decades.

The U.S. government's new antivaccine stance has significant implications for the vaccine makers like Moderna, whose messenger RNA-based technology a number of new committee members raised concerns about during the first day of the meeting on Tuesday. It also could point to disruptions in the influenza vaccine market, dominated by companies like GSK and Sanofi.

This week's ACIP meeting did recommend the use of one vaccine-like product, a new antibody shot from Merck antibody that can prevent respiratory syncytial virus in infants. Two of the seven committee members voted against the recommendation.

Debates over the potential risk posed by thimerosal raged in the late 1990s and early 2000s. Its use has declined markedly. Today, all vaccines for children aged 6 and younger are available in versions with no thimerosal. Though thimerosal is a compound that contains mercury, the form of mercury it contains is different from the more dangerous type found in fish.

"What's the point?" said Dr. Paul Offit, a former member of ACIP, in an interview with Barron's on Thursday morning. Banning thimerosal from flu vaccines would have very little impact, he said, given how few thimerosal-containing vaccines are used in the U.S. "The point is to once again raise the notion that there are components in vaccines that are dangerous, because that's RFK's goal; it's to make vaccines less available, less affordable, more feared. So that's what this is all about."

Meissner, the sole vote against the new recommendations against thimerosal, argued forcefully against his new colleagues, to little effect. "The ACIP makes recommendations based on scientific evidence as much as possible," Meissner said. "And there is no scientific evidence that thimerosal has caused a problem."

Martin Kulldorf, the committee's new chair, argued for the committee to recommend against the use of the preservative. "We know that mercury is a toxin," he said. "We should try to minimize exposure to mercury."

The antivaccine advocate who gave the presentation against thimerosal, Lyn Redwood, said during her presentation that "more than 60,000" pregnant women on Medicaid received vaccines with thimerosal during the 2019-2020 flu system. Later in the meeting, Kulldorff read a note correcting Redwood, saying that according to the CDC, the "Medicaid number" is "greater than 30,000" pregnant women.

Redwood, former president of the antivaccine group Children's Health Defense, which Kennedy founded, said that she was presenting before ACIP as a "private citizen," though CBS News reported Wednesday that she had recently been hired to work at the CDC.

CDC staff earlier this week posted a review paper to the ACIP docket citing extensive research that shows no link between thimerosal and autism. That review paper was later removed from the CDC website, as Barron's reported Wednesday. When a nonvoting committee member asked about the CDC review paper during the Thursday meeting, one of the committee members, Dr. Robert Malone, said: "My understanding is that article was not authorized by the office of the Secretary and has been removed." Kulldorf, the chair, said that all committee members had received the paper.

Non-voting members who spoke during the discussion objected to the process under which the committee was preparing to vote on a recommendation on thimerosal, saying there should have been a presentation from CDC staff and further analysis before a vote on the issue.

"I think it's inappropriate to dismiss a presentation just because a person does not have a PhD or an MD," Kulldorf said in response, referring to Redwood.

In response to a question from a committee member, a representative from the Food and Drug Administration, a political appointee named Dr. Tracy Beth Høeg said that if flu vaccines containing thimerosal weren't allowed next year, "it does not look like we would be limited in terms of availability" of influenza vaccines. Thimerosal is only used in flu shots that come in multi-dose vials.

Write to Josh Nathan-Kazis at josh.nathan-kazis@barrons.com

This content was created by Barron's, which is operated by Dow Jones & Co. Barron's is published independently from Dow Jones Newswires and The Wall Street Journal.

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June 26, 2025 14:28 ET (18:28 GMT)

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