Vaccine advisers recently appointed by Health Secretary Robert F. Kennedy Jr. voted on Thursday to stop recommending flu vaccines containing thimerosal, a mercury-based preservative used to prevent bacterial contamination, to children and pregnant women.

The vote signals a powerful shift in the way federal officials approach vaccines and delivers on Mr. Kennedy’s promise to take a harder look at routine immunizations, particularly those given to children and pregnant women.

“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 meeting and the subsequent vote marked the clearest signs of the unraveling of the decades-long processes that have guided decisions about who get immunized and when.

“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 earlier this month.

Dozens of studies have shown thimerosal to be harmless, and it has not been a component of most childhood shots since 2001. Yet Mr. Kennedy and other critics have long insisted that the preservative might be linked to rising rates of autism.