The chairman of the Senate health committee, in his first significant break with Health Secretary Robert F. Kennedy Jr., has called for a delay in this week’s meeting of a panel of vaccine advisers, saying the group Mr. Kennedy appointed lacks the experience and diversity of opinion necessary to ensure public faith in its recommendations.

The chairman, Senator Bill Cassidy, Republican of Louisiana, made his comments in a social media post on Monday night. Mr. Cassidy, a physician and a strong proponent of vaccines, voted reluctantly to confirm Mr. Kennedy after announcing that the secretary had agreed to consult with him on significant matters and not to disband the advisory committee. The senator has carefully parsed his words about Mr. Kennedy.

“Although the appointees to ACIP have scientific credentials, many do not have significant experience studying microbiology, epidemiology or immunology,” Mr. Cassidy wrote, using the acronym for the Advisory Committee on Immunization Practices, which advises the Centers for Disease Control and Prevention.

“In particular,” Mr. Cassidy added, “some lack experience studying new technologies such as mRNA vaccines, and may even have a preconceived bias against them.”

Mr. Kennedy, who has complained that committee members he fired were too close to the drug industry, defended the dismissals on Tuesday when he appeared before a House subcommittee to defend a budget blueprint for his department that called for major cuts. The health secretary called the old panel “a template for medical malpractice” during a fiery clash with Representative Frank Pallone Jr., Democrat of New Jersey.

He then accused Mr. Pallone of being influenced by drug industry contributions to his campaigns, saying the lawmaker’s “enthusiasm” for the previous panel seemed to be “an outcome of those contributions.