The Centers for Disease Control and Prevention (CDC) experienced notable leadership transitions over the past several weeks, including the firing of Dr. Susan Monarez as CDC Director. These developments drew attention from public health professionals and members of Congress. Yesterday, the Senate Finance Committee also invited Department of Health and Human Services Secretary (HHS) Robert Kennedy Jr. to testify on the issue. The resignations have raised questions in the health policy community about how these changes may affect CDC’s ability to carry forward its wide range of responsibilities, from disease surveillance and outbreak response to chronic disease prevention and health promotion. 

Senior Leadership Departures 

In August, HHS announced the departure of Dr. Susan Monarez as CDC Director. Dr. Monarez was confirmed in July 2025 to serve in that role. With a background in microbiology and science policy, she was the first director in decades to bring a research-based rather than a medical practice background to the position. Her departure occurred after differences emerged regarding policy direction and staffing, particularly in relation to vaccine policy and the firing of 17 members of an Advisory Committee on Immunization Practices. In an op-ed published in the Wall Street Journal yesterday, Dr. Monarez stated, “I served for 29 days as director of the Centers for Disease Control and Prevention. The Senate confirmed me to ensure that unbiased evidence serves our nation’s health, and for doing that, I lost my job. America’s children could lose far more.”  

Following Dr. Monarez’s dismissal, several senior CDC officials, including the Chief Medical Officer and the directors of the National Center for Emerging Infectious Diseases, the National Center for Immunization and Respiratory Diseases, and the Office of Public Health Data and multiple division leaders, announced their resignation.  

Broader Context and Stakeholder Response 

The recent turnover is taking place within a broader conversation about the role of science, governance and public health in the United States. Stakeholders, including professional medical associations, nursing organizations and public health groups, have voiced concern about ensuring that the CDC remains grounded in evidence-based practice. Many have emphasized the importance of continuity in leadership to maintain public trust and institutional stability. 

On Wednesday, more than 1,000 current and former HHS employees sent a letter to members of Congress calling for Kennedy’s resignation. These concerns reached Capitol Hill, where the Senate Finance Committee summoned Secretary Kennedy to testify. Over a period of three hours, several senators including Senator Bill Cassidy (R-LA), questioned the Secretary. Sen. Cassidy noted the obstacles that some Americans are already facing to obtain vaccines, with pharmacies in some states requiring patients to get a prescription. The Secretary denied all allegations, stating that he’s not taking away any vaccines and “any confusion” about access is not his fault. He said the Agency shake-up was “absolutely necessary” to restore the CDC to its “gold standard” of protecting Americans from infectious diseases. “We are the sickest country in the world. That’s why we have to fire people at the CDC. They did not do their job,” Kennedy said. 

Appointment of Acting Director Jim O’Neill 

Jim O’Neill, the Agency’s Deputy Secretary, was appointed Acting CDC Director. Mr. O’Neill recently served as the HHS deputy secretary. Prior roles with the federal government include principal associate deputy secretary from 2007 to 2008 and speech writer for HHS during former President George W. Bush’s administration. He has ties to technology and innovation sectors, briefly serving as CEO of the SENS Research Foundation, an anti-aging organization. Public health professionals have noted that while Mr. O’Neill doesn’t have formal training in medicine or epidemiology, he is well prepared to manage the Agency through a period of transition.