An advisory panel recently appointed by Health Secretary Robert F. Kennedy Jr. voted Thursday to walk back long-standing recommendations for flu vaccines containing an ingredient that the anti-vaccine movement has falsely linked to autism.

The vote signaled a powerful shift in the way federal officials approach vaccines, putting into action Kennedy’s deep skepticism about their safety and delivering the first blows to a scientific process that for decades has provided effective vaccines to Americans.

Kennedy fired all 17 experts on the panel about two weeks ago, and then appointed eight new members, at least half of whom have expressed skepticism about some vaccines.

“We came to this meeting with no predetermined ideas, and will make judgments as if we are treating for our own families,” the panelists said in a statement.

To critics, the two-day meeting of the Advisory Committee on Immunization Practices in Atlanta offered the clearest signs yet that the Trump administration intends to unravel the system that has long guided clinical decisions about vaccination.

“As a physician and scientist who has devoted my entire career to vaccines and preventing and treating infections, this meeting has been devastating to watch,” said Dr. Lakshmi Panagiotakopoulos, an expert on vaccines who resigned from the Centers for Disease Control and Prevention this month.

Thimerosal in question

Dozens of studies have shown that thimerosal, the vaccine ingredient being discussed, is harmless. It has not been a component of most childhood shots since 2001.

“The risk from influenza is so much greater than the nonexistent risk as far as we know from thimerosal,” said the lone dissenter, Dr. Cody Meissner, a professor of pediatrics at Dartmouth Geisel School of Medicine who is widely considered to be the most qualified member of the new committee.

“I find it very hard to justify” the panel’s decision, he added.

In a separate vote, the panel, known as ACIP, recommended seasonal flu vaccines to all Americans 6 months and older. The common single-dose flu shots do not contain thimerosal.

The committee’s power

The committee advises the CDC on vaccine efficacy and safety, and makes recommendations regarding who should receive a vaccine and when.

Insurance companies and government programs like Medicaid are required to cover immunizations that the CDC recommends, and states base their school mandates on the agency’s guidance.

In addition to certain flu vaccines, some panelists on Thursday questioned the safety of other products that have already been approved by the Food and Drug Administration and thoroughly vetted by independent experts.

Others seemed unaware of basic information about the Vaccines for Children program, which provides free immunizations to roughly half of all American children.

“It’s striking how little the voting members seem to know about the diseases and vaccines that they are discussing,” said Dr. Adam Ratner, a pediatric infectious diseases specialist and expert on vaccine policy.

Off-the-record conversations

During the deliberations on a vaccine for respiratory syncytial virus, known as RSV, one of the panelists, Dr. Robert Malone, said that there had been “very, very active discussion and consideration within the committee, just for the record, concerning this product.”

“It has been very actively debated internally,” he said.

Outside experts interpreted his remarks to mean that panelists had been privately discussing the topic among themselves, something that they are not legally allowed to do.

A spokesperson for the Health and Human Services Department said that Malone had been referring to a one-on-one conversation between himself and another panelist, which was “permissible.”

Anti-vaxxer presents

Presentations at the meetings are generally made by CDC staff members. But among the speakers Thursday was Lyn Redwood, a former leader of Children’s Health Defense, the anti-vaccine group founded by Kennedy.

Redwood, who has been hired as a special employee at the Health and Human Services Department, alleged in the meeting that thimerosal was toxic and dangerous to children. (She said that she was making the comments as “a private citizen.”)

A review of evidence demonstrating the safety of thimerosal was posted online by CDC scientists Tuesday but taken down shortly thereafter.

“Giving someone like Lyn Redwood a voice at the ACIP meeting to spread misinformation about a long-settled matter of vaccine safety is yet another troubling way in which RFK Jr. is inappropriately interfering with the CDC vaccine policy process,” said Dr. Fiona Havers, who resigned last week from her position as a senior CDC adviser on vaccine policy.