The White House said late Wednesday it had dismissed Centers for Disease Control and Prevention Director Susan Monarez, installed only four weeks ago, after determining she was “not aligned” with President Donald Trump’s Make America Healthy Again agenda. Monarez’s lawyers contend the action is legally deficient because only the president can remove a Senate-confirmed official, and they maintain she remains in the post. US Health and Human Services Secretary Robert F. Kennedy Jr. defended the shake-up on Thursday, calling the CDC burdened by a “deeply embedded malaise” and saying the agency must more closely reflect the administration’s priorities. Within hours of Monarez’s ouster, at least four veteran leaders—Demetre Daskalakis, Debra Houry, Daniel Jernigan and Jennifer Layden—resigned, stripping the public-health agency of decades of expertise. In public resignation letters, several departing officials said the CDC was being used to advance policies that do not reflect scientific evidence, making continued service “untenable.” Their departures follow earlier layoffs and a shooting at CDC headquarters this month, deepening concern about morale and operational readiness. The leadership vacuum comes as Kennedy accelerates a broad reassessment of US vaccination policy. He has replaced the CDC’s external vaccine-advisory panel, narrowed immediate eligibility for updated COVID-19 boosters to people 65 and older or those with high-risk conditions, and signaled a comprehensive review of the childhood immunization schedule—moves that have unsettled medical groups and vaccine manufacturers. Senator Bill Cassidy, the top Republican on the Senate Health Committee, said the exodus demands congressional oversight. Kennedy is slated to testify before the Senate Finance Committee on Sept. 4, where lawmakers are expected to press him on the agency’s turmoil and its implications for the nation’s preparedness against infectious-disease threats.