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

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

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.

Scientists were slow to recognize that Covid spreads through the air. Some are now trying to get ahead of the bird flu.

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?

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.

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

In its original form, the virus survives in just two countries. But a type linked to an oral vaccine used in other nations has already turned up in the West.

Outbreaks among the unvaccinated are a predictable consequence of falling immunization rates. But even vaccinated adults may be vulnerable to some illnesses.

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 deceased was over 65 and had other medical conditions, state officials said.

Tiny genetic alterations could help the bird flu virus enter cells in the upper respiratory tract, the C.D.C. said. But there is no sign that mutations are widespread in nature.

In crowded Kinshasa, two strains of mpox are sweeping through a community that relies on selling sex. Hundreds of thousands of vaccines sent to the country have not been used.