The firing of Centers for Disease Control and Prevention Director Susan Monarez and abrupt departures of other CDC leaders have left the nation's premier public health agency in turmoil.

The White House fired Monarez on Wednesday, Aug. 27 amid disagreements with Health and Human Services Secretary Robert F. Kennedy Jr. Other top CDC officials announced their resignations the same day.

The leadership shakeup represents an "extraordinary and systematic dismantling of the very top of our nation's public health system," said Richard Besser, a CDC director under presidents George W. Bush and Barack Obama.

Besser disclosed that Monarez told him she was targeted after she refused to fire senior CDC leaders and rubber stamp recommendations by Kennedy's revamped vaccine advisory panel.

The high-profile departures "will require oversight," Senate Committee on Health, Education, Labor and Pensions Chairman Bill Cassidy said in a post on X Wednesday. Sen. Cassidy, a Louisiana Republican, delivered one of the key votes to confirm Kennedy as health secretary earlier this year.

On Thursday, Cassidy called for a federal vaccine advisory panel to postpone its Sept. 18 meeting to allow a review of "serious allegations" regarding the panel.

Kennedy, meanwhile, will first face questions from another Senate committee. He's scheduled to appear before the Senate Finance Committee on Thursday, Sept. 4.

Monarez refused two things before she was fired

Monarez, a federal government scientist, was confirmed by the Senate on July 29 to lead the CDC after President Donald Trump nominated her earlier this year. She was sworn in by Kennedy on July 31.

She took the position after Kennedy, a vaccine skeptic, fired all 17 members of key vaccine advisory panel on June 9. A few days later, Kennedy appointed eight members, including some vaccine skeptics, to the Advisory Committee on Immunization Practices.

Soon after taking office, Monarez learned her tenure would be short-lived.

Attorneys for Monarez said she was targeted because she refused to "rubber-stamp unscientific, reckless directives and fire dedicated public health experts."

The White House notified her on Aug. 27 that she had been terminated, but attorneys for Monarez said the White House didn't follow protocol. Only President Trump can fire a presidential-appointed, Senate-confirmed officer, her attorneys said.

During a briefing Aug. 28, White House Press Secretary Karoline Leavitt said it was Trump who fired Monarez after she refused to step down when Kennedy asked her to resign.

"The president has the authority to fire those who are not aligned with his mission," Leavitt said.

During a call on Wednesday, Aug. 27, Monarez told Besser there were two lines she wouldn't cross. She wouldn't do anything illegal, and she wouldn't defy science. So when she refused Kennedy's request to fire her senior leaders and automatically sign off on Kennedy-appointed vaccine panel recommendations, she knew she would be ousted.

"She was not going to do either of those things," said Besser, the CEO of the health-focused nonprofit Robert Wood Johnson Foundation.

Other key leaders resign from CDC

Other key CDC officials also announced their resignations on Aug. 27.

Demetre Daskalakis, the agency's top official overseeing immunization and respiratory diseases, explained his resignation in a letter posted on X.

He said he could no longer be part of an "environment that treats CDC as a tool to generate policies and materials that do not reflect scientific reality and are designed to hurt rather than to improve the public’s health."

He said recent CDC changes to the adult and children’s immunization schedule "threaten the lives of the youngest Americans and pregnant people."

He also said he and his staff never got the opportunity to brief Kennedy on key public health challenges such as measles, bird flu and the respiratory virus season.

"I am not sure who (Kennedy) is listening to, but it is quite certainly not to us," Daskalakis wrote in his resignation letter. "Unvetted and conflicted outside organizations seem to be the sources HHS use over the gold standard science of CDC and other reputable sources."

CDC Chief Medical Officer Debra Houry and National Center for Emerging and Zoonotic Infectious Diseases Director Daniel Jernigan also announced their resignations.

Besser said the key leaders who resigned were "an important part of the brain trust" that protected Americans' and the world's health. With their departures, "we are in much worse shape than we were a day ago," Besser said.

What's next for the CDC and Kennedy?

Kennedy has long said federal health agencies are too close to the pharmaceutical and medical industries they oversee.

"The CDC has problems," he said in an interview on Aug. 28 with Fox & Friends.

During the interview, Kennedy criticized an agency website that lists vaccines among the 10 greatest advances in medicine. He said there's "a deeply, deeply embedded, I would say, malaise at the agency."

State health departments and doctors groups such as the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists criticized Kennedy in May when he announced intentions to stop recommending the COVID-19 vaccine during pregnancy and for healthy children.

In July, the pediatrics group announced their own guidance on childhood vaccinations, including COVID-19 immunizations.

The CDC has traditionally served as the "quarterback" of the nation's public health system, Besser said, making key recommendations based on medical evidence. But given the controversy over revamped vaccine recommendations and the exit of career scientists, Besser said other medical groups might need to play a greater role in advising medical professionals and patients.

"We are going to see other institutions fill the void," Besser said.

This article originally appeared on USA TODAY: There's a major CDC shakeup underway. What's going on?

Reporting by Ken Alltucker, USA TODAY / USA TODAY

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