The Centers for Disease Control and Prevention is facing a leadership upheaval — and at the center of the shakeup is concern about the agency’s approach to vaccines and U.S. public health.

The White House on Thursday said President Donald Trump had fired CDC Director Susan Monarez after she refused to resign. Lawyers for Monarez said she was “targeted” for “protecting the public over serving a political agenda.”

Meanwhile, four other top health officials at the CDC announced Wednesday they were quitting the agency. That includes Demetre Daskalakis, director of the National Center for Immunization and Respiratory Diseases, who said he could no longer serve because of the “weaponizing of public health.”

The loss of those respected leaders and efforts to oust Monarez follow a string of measures by Health and Human Services Secretary Robert F. Kennedy Jr. – a prominent vaccine skeptic – to overhaul federal health agencies and change immunization policy in the U.S. That includes mass firings, gutting a key government vaccine panel, canceling studies on mRNA shot technology and hiring those with like-minded views.

Kennedy has a long track record of making misleading and false statements about the safety of vaccine shots, but in his current role, he wields enormous power over the agencies that regulate the immunizations and determine both who can get them and which ones insurance plans should cover.

Dr. Georges Benjamin, executive director of the American Public Health Association, said the leadership overhaul at the CDC represents Kennedy’s “failed leadership and reckless mismanagement,” adding that he has a “blatant disregard for science and evidence-based public health.” 

The agency is also reeling from funding cuts and an Aug. 8 attack by a gunman at its headquarters in Atlanta.

Some health policy experts said the leadership exodus could further erode the public’s trust in an agency that is responsible for detecting disease outbreaks and guiding state and local health departments when needed.

“This has to be seen on top of a raft of ways that CDC has been weakened and undermined, maybe irreversibly,” Lawrence Gostin, professor of public health law at Georgetown University, told CNBC. 

“Throughout all of those years, CDC has been independent and the jewel in the crown of American science. That’s literally all crumbling as we speak,” he said. “This is almost the definition of politics undermining science.”

In May, Kennedy said the CDC removed Covid vaccines from the list of shots recommended for healthy pregnant women and children. An updated guidance days later said shots “may” be given to those groups.

Daskalakis said the data analyses that supported the change have “never been shared with the CDC despite my respectful requests to HHS and other leadership.” He also said HHS circulated a “frequently asked questions” document written to support Kennedy’s decision without input from CDC subject matter experts, and that it cited studies “that did not support the conclusions that were attributed to these authors.”

On Wednesday, the Food and Drug Administration approved the latest round of Covid vaccines only for those at higher risk of serious illness, marking another shift in policy around those shots since the pandemic began.

Shares of Covid vaccine makers dipped on Thursday. Moderna’s stock fell more than 3%, while shares of Pfizer fell around 2%. 

Those companies and other drugmakers have been bracing for changes to vaccine and public health policy since Trump first named Kennedy as his pick to lead HHS in November. The CDC’s leadership shakeup only adds to the uncertainty in the pharmaceutical industry, which is also grappling with Trump’s drug pricing policies. 

Kennedy tried to distance himself from his previous views about vaccines and other health policies during his Senate confirmation hearings back in January, claiming that he isn’t “anti-vaccine” and would not make it “difficult or discourage people from taking” routine shots for measles and polio.

But some of Kennedy’s recent efforts appear to reflect his vaccine-critical views. For example, Kennedy in August argued that mRNA vaccines – the technology used in Covid shots – are ineffective and advocated for the development of other jabs that use other “safer” platforms.

Years of research support the effectiveness of mRNA Covid vaccines, and the technology is now approved for use in shots against respiratory syncytial virus.