A scientific meeting on vaccines, which will begin at the Centers for Disease Control and Prevention’s campus in Atlanta on Wednesday, promises to be nothing like previous ones.

Health Secretary Robert F. Kennedy Jr., a longtime vaccine skeptic, fired all 17 members of the agency’s Advisory Council on Immunization Practices just two weeks ago. He replaced them with eight new members, at least half of whom have expressed some skepticism about vaccines.

On Monday, Senator Bill Cassidy, Republican of Louisiana, said on X that the panelists did not have the experience and expertise needed to evaluate vaccines and called for delaying the meeting until the committee was “fully staffed with more robust and balanced representation — as required by law — including those with more direct relevant expertise.

By Tuesday night, one of the eight, Dr. Michael Ross, had stepped down, according to a senior official with knowledge of the situation. Dr. Ross was no longer listed as a member of the committee on the agency’s website.

At the moment, the meeting is likely proceed as planned.

Over the next two days, the panelists are scheduled to debate the pros and cons of some new vaccines, and to reconsider some questions that were long thought to have been settled. The panel’s decisions may upend the availability of vaccines to the most vulnerable Americans, including young children, older adults and pregnant women.