WASHINGTON >> The Biden administration, keeping a watchful eye on an outbreak of avian influenza that has led to the deaths of tens of millions of chickens and is driving up the cost of eggs — not to mention raising the frightening specter of a human pandemic — is contemplating a mass vaccination campaign for poultry, according to White House officials.

The bird flu outbreak, which began early last year, is the biggest in the nation’s history, affecting more than 58 million farmed birds in 47 states, as well as birds in the wild. It has already spilled over into mammals, such as mink, foxes, raccoons and bears, raising fears that the virus that causes it, known as H5N1, could mutate and start spreading more easily among people.

Experts at the Centers for Disease Control and Prevention, whose focus is human health, say the risk of a pandemic is low. As a precaution, the agency has sent drug manufacturers flu virus samples that could form the basis of vaccines for people. The CDC is also exploring whether commercial test manufacturers would be willing to develop tests for H5N1, similar to those used for the coronavirus.

Bird flu infections in humans are rare, and transmission of bird flu between humans is extremely rare. Cases typically involve people exposed to poultry. In the United States, the CDC, in partnership with state and local public health departments, is monitoring people who are exposed to H5N1.

Farm birds are already vaccinated against infectious poultry diseases, such as fowlpox. But an avian influenza vaccination program would be a complex undertaking, and poultry trade associations are divided over the idea, in part because it might spawn trade restrictions that could destroy the $6 billion poultry export industry. Dr. Carol Cardona, an expert on avian health at the University of Minnesota, said that the fear of trade bans was a huge barrier to the mass vaccination of poultry.

“This is the undeclared war — trade,” Cardona said.

White House officials, speaking on the condition of anonymity to discuss internal deliberations, say that vaccinating poultry is not the only step they are considering. More immediately, they are focused on encouraging poultry farms to prevent transmission of the virus through biosecurity measures like enhanced disinfection procedures for their workers.

A handful of countries in which avian influenza is endemic, including China, Egypt and Vietnam, already routinely vaccinate poultry against it.

This article originally appeared in The New York Times.

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