Senator Bill Cassidy cast doubt Wednesday on vaccine advisers handpicked by Secretary Robert F. Kennedy Jr. and changes they could make to childhood vaccine guidance.

Asked whether, if the vaccine advisory panel recommends changes to the childhood vaccine schedule in its meetings this week, the American people could have confidence in that decision, Mr. Cassidy answered with a flat “No.”

Secretary Kennedy fired all 17 members of the committee in June and replaced them with his own lineup of advisers. The panel, while unknown to the majority of the American public, recommends which shots they should get and when. The C.D.C. director reviews the panel’s recommendations and usually accepts them. The outcome influences state decisions on mandatory shots for school children and insurance coverage.

The panel is set to meet and offer new recommendations on vaccines like those for Covid-19, hepatitis B and measles on Thursday and Friday of this week.

Mr. Cassidy, the chairman of the Senate health committee and a doctor who is a specialist in liver disease, told reporters on Capitol Hill that vaccinating newborns against hepatitis B, which causes liver damage, had brought the number of children with the disease each year down from 20,000 cases to around 20.

“It’s not a mandate,” said Mr. Cassidy. “You give the mother the option.”

Secretary Kennedy has cast doubt on whether babies should continue to receive the vaccine on the day of their birth. The advisory panel has recommended the vaccine for decades.

Mr. Cassidy voiced concern that patients would have to pay out of pocket for the hepatitis B shot if the panel removed it from the recommended childhood vaccines.

“So it becomes a financial hardship,” he said, adding, “You always have to balance the patient’s pocketbook with their health.”

Susan Monarez, the former head of the Centers for Disease Control and Prevention, testified Wednesday before the Senate health committee that Mr. Kennedy had directed her to approve the committee’s vaccine recommendations “regardless of the scientific evidence,” and to dismiss, “without cause,” C.D.C. scientists who work on vaccine policy.

She warned that the advisory panel’s recommendations could end up restricting vaccine access for children and others in need.

“The stakes are not theoretical,” Dr. Monarez said Wednesday, adding, “If vaccine protections are weakened, preventable diseases will return.”