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

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.

Avian influenza has led to a shortage of eggs and wholesale prices that are through the roof. Consumers can expect to feel the pain for a while.

The cases have spurred new pet food safety rules and poultry surveillance efforts.

The highly infectious H5N1 strain has caused outbreaks across the country. Now, Long Island’s last duck farm must kill its entire flock and may go out of business, its owner said.

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

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

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.

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.

New federal rules call for testing unpasteurized milk from dairy processors and for farm owners to provide details that would help officials identify and track cases more easily.

© Tim Gruber for The New York Times

On America’s large dairy farms, milking is a vast operation, and the potential for disease transmission is worrying, health experts say.

© Tim Gruber for The New York Times