Sen. Bill Cassidy, R-La., on Monday criticized Health and Human Services Secretary Robert F. Kennedy Jr.’s picks for a key federal vaccine advisory committee and called for the group’s next meeting to be delayed until more members with relevant expertise can be appointed.

Kennedy abruptly fired all 17 members of Centers for Disease Control and Prevention’s visory Committee on Immunization Practices this month and replaced them with eight new members, including known vaccine skeptics. That group is scheduled to meet for the first time Wednesday and Thursday.

Cassidy, a medical doctor who is the chairman of the Health, Education, Labor and Pensions Committee, was a key vote in Kennedy’s confirmation. He said he voted for Kennedy after Kennedy made a number of commitments, including not to make changes to ACIP, a highly influential panel that makes vaccine recommendations and shapes the childhood vaccination schedule.

Cassidy expressed concerns Monday on X about the newly appointed members.

“Although the appointees to ACIP have scientific credentials, many do not have significant experience studying microbiology, epidemiology or immunology. In particular, some lack experience studying new technologies such as mRNA vaccines, and may even have a preconceived bias against them,” Cassidy wrote.

“Wednesday’s meeting should not proceed with a relatively small panel, and no CDC Director in place to approve the panel’s recommendations. The meeting should be delayed until the panel is fully staffed with more robust and balanced representation—as required by law—including those with more direct relevant expertise,” he continued.

Susan Monarez, President Donald Trump’s pick for CDC director, will have her Senate confirmation hearing Wednesday. Without a CDC director, Kennedy has signed off on some ACIP recommendations. And last month, without input from ACIP, he announced that the Covid vaccine would no longer be recommended for healthy children and pregnant women.

The Department of Health and Human Services, which oversees the CDC, did not immediately respond to a request for comment. HHS spokesperson Andrew Nixon previously defended Kennedy’s ACIP picks, saying in a statement that the new panel “includes highly credentialed scientists, leading public-health experts, and some of America’s most accomplished physicians. All of these individuals are committed to evidence-based medicine, gold-standard science, and common sense.”

A draft agenda for this week’s ACIP meeting includes a discussion and a vote on flu vaccines that contain thimerosal, a form of mercury that had been used as a preservative in some vaccines. Kennedy has long espoused the debunked claim that there is a link between thimerosal and autism.

Since 2001, nearly all vaccines made in the United States contain no thimerosal or only trace amounts. Only multi-dose flu shot vials still contain the preservative. Most flu shots now come in single-shot packaging.