Worrisome bird flu mutations in two patients — one in Louisiana and another in Canada — underscore the growing threat of severe H5N1 avian influenza illnesses in humans.
In the 65-year-old Louisiana patient’s case, the mutation was likely not present in wild birds, according to CDC researchers. Genetic sequencing showed the virus to be different than the strain found in a backyard poultry flock that infected the patient.
A teenager from British Columbia, Canada, whose case was discussed in a special edition of the New England Journal of Medicine exploring H5N1 cases in North America in 2024, also became severely ill with a mutated version of the virus. The source of the virus that sickened the teen is unknown.
The severity of both patients’ illnesses is “concerning,” according to the CDC, which said mutations may allow the virus to better bind to humans’ upper airways and make it easier to jump from person to person, which hasn’t happened before.
Still, the CDC said, the risk to humans in the current bird flu outbreak “has not changed and remains low.”
The agency added, “These changes would be more concerning if found in animal hosts or in early stages of infection (e.g., within a few days of symptom onset) when these changes might be more likely to facilitate spread to close contacts.”
Here are seven things to know:
As of Dec. 31, 66 U.S. human bird flu cases have been reported to the CDC. Most have described as “mild” cases that didn’t require hospitalization. No humans have died of bird flu infections.
Importantly, the CDC said, there’s no evidence the virus spread from the patient in Louisiana to other people, and the samples taken may not be enough on their own to enable the virus to jump from human to human.
But there have been human cases of bird flu in which the origin is unknown, including the teen in Vancouver, British Columbia, and patients in Missouri and California.
Co-infections pose a greater risk as the flu season continues, according to health experts.
Seasonal flu vaccines don’t protect against bird flu viruses, but can reduce the risk of a seasonal flu and bird flu co-infection. Having both inflections at once could allow the viruses to swap genes and to jump from human to human as efficiently as seasonal flu does, according to health officials.
Michael Osterholm, a University of Minnesota infectious disease researcher, likened binding interaction of the bird and human influenza strains to a lock and key. To enter a cell, the virus needs to have a key that turns the lock, and this finding means the virus may be changing to have a key that might work.
“Is this an indication that we may be closer to seeing a readily transmitted virus between people? No,” Osterholm told The Associated Press. “Right now, this is a key that sits in the lock, but it doesn’t open the door.”
Still, the mutations re concerning.
“If there are all these people getting infected, that provides so many opportunities for the virus to better adapt,” Dr. Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada, told The New York Times.
“It has the potential to really harm a lot of people,” she said.
The CDC has downplayed concerns that bird flu, especially if the virus further mutates and makes people sicker, could spread to pandemic levels. Scientists should continue to follow what’s happening with mutations carefully, Osterholm told The AP.
“There will be additional influenza pandemics and they could be much worse than we saw with COVID,” he said. “We know that the pandemic clock is ticking. We just don’t know what time it is.”
Although no human-to-human cases of H5N1 have been confirmed, “this feels the closest to an H5 pandemic that I’ve seen,” Louise Moncla, a virologist at the University of Pennsylvania, told Science.
Seema Lakdawala, a flu researcher at Emory University, concurred, telling Science, “If H5 is ever going to be a pandemic, it’s going to be now.”
Other researchers were more optimistic, pointing out that similar viruses, such as one called H7N9, ran their course and this one could do the same.
“Why didn’t H7N9 end up being easily human-to-human transmissible and cause a pandemic?” Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security told Science. “I feel like there’s really no way to estimate and it could go either way.”
The CDC has faced blistering criticism for its response to the outbreak.
“We kind of have our head in the sand about how widespread this is from the zoonotic standpoint, from the animal-to-human standpoint,” Dr. Deborah Birx, the White House coronavirus response coordinator under President Donald Trump, told CNN late last month.
Wider testing of farmworkers is needed, especially as the flu season ramps up, Birx said.
The CDC pushed back, telling CNN in a statement that “comments about avian flu (H5N1) testing are out of date, misleading and inaccurate.”
“Despite data indicating that asymptomatic infections are rare, CDC changed its recommendations back in November to widen the testing net to include testing asymptomatic people with high-risk exposure to avian flu, and during the summer, it instructed hospitals to continue subtyping flu viruses as part of the nationwide monitoring effort, instead of the normal ramping down of surveillance at the end of flu season,” the spokesperson said.
“The result: more than 70,000 specimens have been tested, looking for novel flu viruses; more than 10,000 people exposed to avian flu have been monitored for symptoms, and 540 people have been tested specifically for H5N1,” the spokesperson continued. “Additionally, CDC partnerships with commercial labs mean that H5N1 tests are now available to doctor’s offices around the country, significantly increasing testing capacity.”
Vaccines for H5N1 bird flu have been developed, but aren’t generally available. Some have been stored in a strategic national stockpile to be deployed in an emergency, and drugmakers have already contracted to make 5 million doses. The Biden administration has said there are no plans to release the bird flu vaccine.
Dr. Leana Wen, a former Baltimore health commissioner, said Sunday on CBS’s “Face the Nation” that before he leaves office, President Joe Biden should make rapid tests available and ask the Food and Drug Administration to authorize the bird flu vaccine for farmworkers and other vulnerable populations.
“I feel like we should have learned our lesson from COVID that just because we aren’t testing, it doesn’t mean that the virus isnt there,” Wen said.
Biden should act now “because we don’t know what the Trump administration will do about bird flu.”
For example, Robert F. Kennedy Jr., Trump’s pick to head the Department of Health and Human Services, and other vaccine skeptics could “hold up” the FDA’s authorization of the vaccine or “withhold testing,” Wen said.
“There’s research done on it. They could get this authorized now, and also get the vaccine out to farmworkers and to vulnerable people,” Wen said.
Bird flu, which has been common for years in wild bird and commercial poultry flocks worldwide, was discovered in U.S. dairy herds for the first time in March 2024. It has since spread to about 900 herds in 16 states. Human bird flu cases have been confirmed in 10 states.
The virus has spread to other animals as well, including the first case in a pig, the U.S. Department of Agriculture said in November.
Also, 20 big cats that died at a federal wildlife sanctuary in Shelton, Washington, tested positive for the virus, and a domestic cat in Oregon died after eating raw turkey in cat food that tested positive for the H5N1 bird flu virus.
Avian influenza has also killed tens of thousands of seals and sea lions in different corners of the world, disrupting ecosystems and challenging scientists who don’t see a clear way to slow the devastating virus.
People can protect themselves against bird flu in several ways, including:
Observe sick and dead wild birds, poultry and other animals from a distance, and wear personal protective equipment if contact is unavoidable;
Avoid contact with surfaces or materials (animal litter or bedding) that may be contaminated with the saliva, mucous or feces of infected wild or domestic birds and other animals with confirmed or suspected infections; and
Avoid contactm with raw milk or raw milk products from infected dairy herds, including consumption of the products.
The Associated Press contributed reporting.
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Credit: Zambezi Conservation
Snares such as these pose a risk to all wildlife.
Credit: Zambezi Conservation
Drones provide a bird’s-eye view to quickly spot injured or at-risk animals.
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