Workers and supporters gather to rally for departing scientific leaders at the Centers for Disease Control and Prevention outside the CDC headquarters on Thursday in Atlanta. (AP Photo/Ben Gray)

NEW YORK (AP) — The nation’s top public health agency was left reeling and leaderless as the White House works to expel its handpicked director from the Centers for Disease Control and Prevention and three senior officials were escorted from its headquarters on Thursday.

The turmoil triggered rare bipartisan alarm as President Donald Trump’s health secretary, Robert F. Kennedy Jr., tries to advance anti-vaccine policies that are contradicted by decades of scientific research.

The chaos comes weeks before a key advisory committee, which Kennedy has reshaped with vaccine skeptics, is expected to meet to issue new recommendations on immunizations.

Two Republican senators called for congressional oversight and some Democrats said Kennedy should be fired. He is scheduled to testify on Capitol Hill on Sept. 4.

Kennedy has not explained the decision to oust Susan Monarez as CDC director less than a month after she was sworn in, but warned that more turnover could be coming.

“There’s a lot of trouble at the CDC and it’s going to require getting rid of some people over the long term, in order for us to change the institutional culture,” Kennedy said at a news conference in Texas.

The White House has only said that Monarez was “not aligned with” Trump’s agenda. There is no word on when a replacement could be named.

Monarez’s lawyers said that she refused “to rubber-stamp unscientific, reckless directives and fire dedicated health experts.” She is fighting her dismissal, saying the decision must come directly from Trump, who nominated her in March.

The saga began Wednesday night with the administration’s announcement that Monarez would no longer lead the CDC. In response, three officials — Dr. Debra Houry, Dr. Demetre Daskalakis and Dr. Daniel Jernigan — resigned from senior roles at the agency.

The officials returned to the office Thursday to collect their belongings, and staff members at the beleaguered agency had planned to gather in the afternoon to applaud them as they left the Atlanta campus. But their removal by security personnel earlier in the morning squelched those plans, according to current and former employees.

Houry and Daskalakis told The Associated Press that Monarez had tried to guard against political meddling in scientific research and health recommendations.