Federal officials have granted emergency approval to an avian flu vaccine for use in California condors, a US Department of Agriculture agency announced on Tuesday.

The move comes after more than a dozen of the critically endangered birds recently died from the virus, known as H5N1. Worldwide, there are fewer than 600 California condors, which can have wingspans of nearly 10 feet. The emergency approval is “an attempt to prevent further deaths of these birds,” said the agency, the Animal and Plant Protection Inspectorate.

It is not yet clear when California condors will begin to be vaccinated, but the effort will begin with captive birds, said Dr. Carlos Sanchez, chief veterinarian at the Oregon Zoo, which has a condor breeding program and plans to vaccinate some of its birds. . The condors will be closely monitored to ensure the vaccine is safe and effective. “But as you can imagine, all of this has to happen quickly so we don’t lose any more birds,” he said.

The virus was first discovered in a California condor was found dead at the end of March. Since then, 20 more condors have died and four more condors are currently in rehabilitation facilities, according to the federal agency. The virus has been confirmed in 15 of these birds.

Condors appear to be “highly susceptible” to the virus, said Dr. Sanchez. “Once they get it,” he said, “they tend to have high mortality.”

California condor populations declined rapidly during the 20th century; in the 1980s, fewer than 30 birds remained. In the decades since, captive breeding programs have helped the population recover. If the virus enters more condor populations, it could erase this progress, Dr. Sanchez: “We’re talking about a potentially catastrophic collapse of the conservation project.”

The H5N1 virus was first detected in China in 1996. Since then, different versions of the virus have circulated in wild birds and caused repeated outbreaks in poultry. A new version of the virus arrived in North America in late 2021. Since then, it has spread rapidly across the United States, causing the largest bird flu outbreak in the nation’s history and resulting in the deaths of almost 60 million farmed birds.

It has also taken a much heavier toll on wild birds than previous outbreaks. It has been discovered in more than 6,700 wild birds – a figure that is surely an underestimate – in every state except Hawaii and has resulted in the mass death of wild birds around the world.

It has, too, repeatedly spilled over to mammals and caused a small number of human infections, usually in people known to have been in close contact with birds. The virus is best adapted to birds, and the threat to the public remains low, officials say. But researchers have long been concerned that viruses can develop in a way that helps it spread easily among people.

The vaccine has only been approved for emergency use in California condors. The small size of the existing California condor population will allow the vaccination program to be closely monitored, the Animal and Plant Health Inspection Service said.

But the size and scope of the current outbreak has prompted officials to do so consider a mass poultry vaccination campaign. USDA scientists have been testing many potential poultry vaccines and have said some results may be available this spring.

The country could see more animal outbreaks in the coming weeks as infected wild birds migrate north for the summer.