The Trump administration laid off thousands of federal health workers Tuesday in a purge that included senior leaders and top scientists charged with regulating food and drugs, protecting Americans from disease and researching new treatments and cures.

Layoff notices began arriving at 5 a.m., workers said, affecting offices responsible for everything from global health to food safety. Some senior officials based in the Washington, D.C., area were reassigned to the Indian Health Service and asked to choose between locations including Alaska, Oklahoma and New Mexico — a tactic to force people out, employees said.

The layoffs and reassignments touch every aspect of the federal Department of Health and Human Services, and are part of what the administration has said is a vast restructuring of the agency. Entire offices, including a vaccine research program aimed at preventing the next pandemic, were wiped out.

Outside experts and former officials said the loss of expertise was immeasurable. Many described it as a “bloodletting.” Hundreds of people, many carrying handmade signs, gathered in the lobby of a National Cancer Institute building in the Maryland suburbs, to witness the exodus of fired employees. Some of the observers and the former employees cried.

But as staff members reeled and comforted one another, Health Secretary Robert F. Kennedy Jr. posted a video on social media that showed him swearing in the new heads of the Food and Drug Administration, Dr. Martin A. Makary, and the National Institutes of Health, Dr. Jay Bhattacharya.

“Welcome aboard,” Kennedy said. “The revolution begins today.”

The cuts were intended to fulfill Kennedy’s plan, announced last week, to shrink his department from 82,000 to 62,000 employees. Tuesday’s layoffs affected 10,000 employees, on top of 10,000 who had already been fired or left voluntarily. The department did not respond to a request for comment on the record.

The restructuring is intended to bring communications and other functions directly under Kennedy, who has vowed to “make America healthy again.” It includes collapsing a number of agencies into a new division called the Administration for a Healthy America. Kennedy said last week that the department was “going to do more with less.”

‘Simply a tragedy’

Layoff notices began arriving at 5 a.m., workers said, affecting offices responsible for everything from global health to medical devices to communications at agencies including the FDA, the NIH and the Centers for Disease Control and Prevention.

“Today was simply a tragedy,” said Michael Osterholm, who directs the University of Minnesota’s Center for Infectious Disease Research and Policy, and has advised presidents of both parties. “There is so much intellectual capital that literally got swept under the rug today in this country, and we are going to pay a price for this for years to come.”

Kennedy is also eliminating entire but lesser known parts of his department, such as the Administration for Community Living, which supports programs that help older Americans and people with disabilities live independently. Advocates for disability rights say the cuts could deprive the most vulnerable Americans of housing, personal care and other services.

Three top congressional Democrats, anticipating the cuts, sent a lengthy letter to Kennedy on Monday demanding that he explain his choices. It was signed by Sen. Patty Murray of Washington, Sen. Tammy Baldwin of Wisconsin and Rep. Rosa DeLauro of Connecticut, all of whom help oversee the health department’s budget.

“Authoritatively stating that these drastic changes will improve the health of Americans without any explanation insults the American public and defies logic,” the lawmakers wrote.

Some are reassigned

Bhattacharya, on his first day of work, sent an email to staff saying the layoffs would “have a profound impact on key NIH administrative functions, including communications, legislative affairs, procurement and human resources.” He expressed his appreciation for the “scientists and staff whose work has contributed to lifesaving breakthroughs in biology and medicine.”

At the NIH, several institute directors — including Dr. Jeanne Marrazzo, head of the National Institute of Allergy and Infectious Diseases, the institute formerly led by Dr. Anthony Fauci — were reassigned to the Indian Health Service. So were Fauci’s wife, Christine Grady, the head of the NIH Office of Bioethics, and Dr. Clifford Lane, a close ally of Fauci’s who oversaw clinical research.

At the FDA, the top tobacco regulator, Brian King, got a similar reassignment.

The health service, responsible for providing federal health services to American Indians and Alaska Natives, is chronically understaffed and underfunded. Kennedy recently lamented that it has been “treated as the redheaded stepchild at HHS” and said President Donald Trump wants him to “rectify this sad history.”

Those who received reassignments to the Indian Health Service were given until Wednesday to decide whether to accept the offer or leave their jobs.

What was cut

Some workers knew they would be affected by the layoffs. At the department headquarters in Washington, officials responsible for minority health and infectious disease prevention were told Friday that their offices were being eliminated, according to employees.

Others were caught off guard. At the FDA, senior leaders were pushed out and offices focused on food, drug and medical device policy were hit with deep staff reductions amounting to about 3,500 agency staff members. On Friday, the agency’s top vaccine regulator, Dr. Peter Marks, was forced to resign under pressure. He lashed out at Kennedy afterward, saying the secretary “doesn’t care about the truth.”

Some FDA workers said they discovered they had been fired when they attempted to scan their badges to get into the building early Tuesday. Other staff members who oversee veterinary medicine and coordinate the complex work of reviewing new drug applications were let go. Additionally, employees of several FDA labs around the United States were cut, including those who test medical products in Detroit and San Juan, Puerto Rico, and those who test food in San Francisco and Chicago.

“The FDA as we’ve known it is finished, with most of the leaders with institutional knowledge and a deep understanding of product development and safety no longer employed,” Dr. Robert Califf, who ran the FDA during the Biden administration, wrote on social media. He said “history will see this” as “a huge mistake.”

At the CDC, which Kennedy wants to pare back to focus only on infectious disease, the reorganization is likely to have immediate effects. Offices devoted to the study of other programs, including reproductive health, chronic disease and gun violence prevention, were disbanded.

The administration has eliminated offices dedicated to protecting workers in various industries, including those that inspect mines for safety. A two-year project to study the effects of radiation was eliminated, as was an ongoing project on lead contamination in Milwaukee.