Thousands of people responsible for tracking health trends and disease outbreaks, conducting and funding medical research, monitoring the safety of food and medicine, and administering health insurance programs for nearly half of the country were laid off Tuesday at the nation’s top health agencies.

The moves will shrink the Department of Health and Human Services to 62,000 positions, lopping off nearly a quarter of its staff — 10,000 jobs through layoffs and another 10,000 workers who took early retirement and voluntary separation offers. Many of the jobs are based in the Washington area, but others are in Atlanta, where the U.S. Centers for Disease Control and Prevention is based, and in smaller offices throughout the country.

The cuts include researchers, scientists, doctors, support staff and senior leaders, leaving the federal government without many of the key experts who have long guided U.S. decisions on medical research, drug approvals and other issues.

Health Secretary Robert F. Kennedy Jr. criticized the department he oversees as inefficient in announcing the cuts last week. Hours after the layoffs began Tuesday he wrote “The revolution begins today!” on social media as he celebrated the swearing-in of two agency heads.

Food and Drug Administration

The FDA, which inspects and sets safety standards for medications, medical devices, tobacco and foods, is set to lose 3,500 staffers.

The notices handed down Tuesday morning impacted FDA workers who review new drug and medical implants, set policy for electronic cigarettes and tobacco products as well as the entire press office staff. The agency’s top tobacco regulator was removed from his post, along with several of his deputies. Other senior officials in the FDA’s centers for drugs and vaccines also said they would leave the agency after being offered reassignments in distant parts of the U.S.

Centers for Disease Control and Prevention

Around 2,400 jobs were expected to be cut from the CDC, which works to prevent diseases caused by infections, genetics, environmental poisons and other causes.

Many of the layoffs reported were in areas involving deaths and injuries from things other than infectious diseases. That included programs that track and prevent asthma, smoking, gun violence, climate change and other health threats. The center that researches and protects worker health was largely decimated, people at the agency said.

At least nine high-level directors were affected, receiving notices that they were being placed on administrative leave and offered a reassignment to another HHS agency, the Indian Health Service. Some public health experts outside the agency saw it as a bid to get veteran agency leaders to resign.

National Institutes of Health

The NIH is the world’s leading medical research agency — funding research into cancer, Alzheimer’s, HIV and other devastating diseases at its own facilities and at universities and labs. It was expected to lose 1,200 jobs on Tuesday.

That’s on top off more than 1,000 NIH employees that the Trump administration already had fired, both scientists and staff who administer billions in research funding. The administration also has canceled hundreds of NIH grants to scientists around the country.

On Tuesday, at least four directors of the NIH’s 27 institutes and centers were put on administrative leave, including a well-known expert on HIV in women who heads the National Institute of Allergy and Infectious Diseases. Other dismissals included scientists involved in brain research, computer specialists and nearly the entire communications staff.

Centers for Medicare and Medicaid

CMS, which oversees Medicare, Medicaid and the Affordable Care Act marketplace, is cutting 300 jobs. Reported cuts so far have focused on the agency’s Office of Minority Health, Office of Equal Rights and Opportunity as well as the Office of Program Operations & Local Engagement.

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