As of Tuesday, 22 children and two adults had been infected, all of whom were unvaccinated, local officials said.

The vote capped a remarkable rise for Robert F. Kennedy Jr., who was confirmed by a Republican Senate in a chamber where his father and uncles once served as Democrats.

The vets had no symptoms, and one worked only in states where no dairy infections had been reported.

Health experts see his retreat from international cooperation as disrupting the safe-keepers of one of the world’s deadliest pathogens.

President Trump’s pause on aid, and the gutting of the primary aid agency, could jeopardize the health of more than 20 million people worldwide, including 500,000 children, experts say.

Vague federal directives have led to frantic action, and perhaps overreaction, before a Friday deadline.

When we face some risk of a bird flu pandemic, do we want to entrust our health to a man who has fought lifesaving vaccines?

Robert F. Kennedy, President Trump’s nominee for health secretary, vigorously defended his views on vaccines, and a key senator still has clear doubts.

Many of the frozen programs are aimed at alleviating disease and malnutrition, but even security programs with U.S. funding are shutting down.

PEPFAR’s computer systems also are being taken offline, a sign that the program may not return, as Republican critics had hoped.

In recent months, bird flu has started raising red flags among scientists and public health officials. Apoorva Mandavilli, a New York Times reporter who covers infectious diseases, explains why we need to start taking bird flu seriously.

A pandemic is not inevitable, scientists say. But the outbreak has passed worrisome milestones in recent weeks, including cattle that may have been reinfected.

R.F.K. Jr. and others have blamed the ingredient for allergies and other illnesses. Scientists say it actually bolsters the immune response.

Scientific meetings were canceled, and research data on the bird flu outbreak was delayed, amid confusion over the directive.

Public health experts say U.S. withdrawal from the W.H.O. would undermine the nation’s standing as a global health leader and make it harder to fight the next pandemic.

President-elect Donald J. Trump’s advisers have spent months trying to identify a disease that will help them build their case for closing the border.

While cases are climbing in China, the situation is very different from what it was when Covid-19 emerged five years ago, medical experts say. HMPV has circulated in humans for decades.

The administration is committing an additional $306 million toward battling the virus, and will distribute the money before President-elect Donald J. Trump takes office.