Biden said he'd follow the science. But sometimes he gets ahead of the experts.

“Everybody uses this statement ‘follow the science’ very glibly, and I think that the science here did not warrant picking out a group of people and saying that you may be at more risk for acquiring an infection,” said Dr. Sarah S. Long, a member of the C.D.C.’s advisory committee, referring to the groups of workers who were made eligible for booster shots.

Dr. Long, who is a professor of pediatrics at Drexel University College of Medicine, said that a president telegraphing his opinion before the formal public health process undermined the expert advisers, calling it a violation of the “checks and balances” built into the system. She also criticized Dr. Walensky for expanding the number of people eligible for the boosters.

If that pattern of reversals were to extend beyond boosters, she said, that “would be the end of the vaccine program as you know it.”

But a number of other committee members — including some who also resisted a broad expansion of the booster program — defended Dr. Walensky’s ruling, adding that federal regulators authorized additional shots less than 24 hours before the C.D.C.’s advisers were asked to give guidance.