As bird flu hits cattle herds in U.S., scientists say these H5N1 factors worry them most
As the H5N1 bird flu virus mutates and rapidly spreads through American cattle herds — a first for the U.S. — doctors and veterinarians are fearful that if the virus is left unchecked, it could spiral into a possible pandemic
Avian influenza is constantly changing. Every new infection increases the odds bird flu could potentially become more deadly or easily transmissible between humans, infectious disease expert Dr. Kamran Khan warns. Today, the virus does not spread person to person, but Khan warns that could change. His company BlueDot was among the first to flag the virus in China that led to the COVID pandemic. Khan said bird flu is just as concerning.
Khan said he wants people to know "this is a very serious threat to humanity" and that the longer bird flu is left to spread, "the greater the risks are going to be."
"We are really at risk of this virus evolving into one that has pandemic potential," Khan said. "And the reality is none of us know whether this is next week, or next year, or never. I don't think it's never. But it may be here far sooner than any of us would like."
Bird flu spreads to cows and humans in the U.S.
Bird flu has circled the globe for decades, but the discovery last year that the deadly pathogen had jumped from a wild bird to a cow upped the stakes. This outbreak has decimated poultry flocks since 2022. Bird flu is so lethal in poultry that more than 160 million birds have been killed during this outbreak, driving egg prices sky high.
The first bird flu detected in cattle was in early 2024. Cows were suffering from a mysterious disease: their fevers spiked, their milk dried up, they were coughing, drooling, and lethargic. Soon, there were more sick cattle in neighboring states.
Colorado veterinarian Dr. Kay Russo joined a conference call of worried vets from several states to try to figure out what was going on. She said she learned birds on Texas farms had also died, that cats were demonstrating neurologic symptoms and that workers were complaining of flu-like symptoms.
Tests confirmed Russo's worst fears: H5N1 had jumped to cattle for the first time.
It's not clear how bird flu is spread from cow to cow, but milking equipment is a prime suspect. The virus is thought to linger on the auto-milker waiting for the next cow.
The virus has continued to rip through America's dairy herds and poultry flocks, and it's jumped to other mammals, including humans. Seventy Americans have caught the virus, with one death reported – in Louisiana in January – in someone who had underlying health conditions. Workers in milking parlors are among those who have fallen sick.
All but two states reported bird flu infections in either cattle, poultry or people between March 2024 and February 2025.
There is also a new strain of the H5N1 bird flu virus, called D1.1, which has been discovered in cattle. It can lead to more severe disease in some people.
"It's a numbers game"
In past outbreaks of H5N1 around the world, bird flu has often been deadly. Despite the urgency, Russo and other vets said the Biden administration was slow to act. It was a month before the U.S. Department of Agriculture required cows to be tested before interstate travel, and 10 months before a raw milk testing program was launched. Today, some states test weekly, some hardly at all.
"At present, we're given a stick, and they put a blindfold on us, and we're sent into a gunfight and we're losing. We are losing," Russo said.
Russo, who is most concerned by the pandemic potential of the virus, warned that the U.S. is running out of time to stop bird flu. She told 60 Minutes her fears about a possible pandemic are the worst case scenario, but at the moment the virus has the upper hand. Russo says the U.S. hasn't done enough testing of animals or humans to know how the virus is spreading.
"I think it's a numbers game, and the more we let it move unchecked, the more likely we're gonna have even a bigger mess on our hands," Russo said.
Bird flu has spread to over 1,000 dairy herds across the country. It has also jumped to dozens of other mammals — a rapid and unprecedented spread, infectious disease physician Khan said.
"And it's showing us that the virus is capable of adaptation. If you allow it, it will just get better and better at infecting other mammals, including potentially humans," Khan said.
Most of the confirmed cases among people in the U.S. have been farmworkers, who have largely had mild symptoms. The Centers for Disease Control and Prevention says the virus still poses a low risk to the general public. But Khan said every new infection increases the odds that bird flu could mutate and lead to more severe disease.
In North America, six people have ended up in hospital with bird flu since March 2024. More worrying, five people had no known exposure to sick animals.
Virologist Dr. Angela Rasmussen said she's alarmed by the way bird flu is jumping to more mammals; every new spillover gives the virus another chance to evolve and possibly start spreading from person to person. There have been cases in foxes, goats, pigs, rats, cats and raccoons.
"The fact that this virus can infect so many different types of mammals is a huge concern in terms of its ability to infect people," Rasmussen said.
It's something she admitted she's worried about.
"I don't sleep very much these days," Rasmussen said.
What's next in the fight against bird flu
Many scientists told 60 Minutes that vaccines could be the best defense. There is a vaccine for bird flu, but it has not been licensed by the Food and Drug Administration. Moderna has a new one, but the Trump administration has paused its final funding. There are vaccines for poultry too, but they haven't been used because many of America's trading partners will not import vaccinated birds.
The USDA's milk testing program offers a glimmer of hope, said Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Lab, which is working with the USDA to test raw milk for H5N1. Pasteurization kills the virus, but raw milk can be loaded with it.
Forty five states are now doing some form of testing on raw milk from farms. Poulsen said it's helped to slow the spread of bird flu in some states.
The CDC is also trying to ramp up its testing, but there's another problem: almost half of farmworkers are undocumented and may be reluctant to be tested.
Rasmussen, who was among the scientists given expert briefings by the Biden administration in 2024, said the Biden administration miscalculated the seriousness of the threat. She said the Trump administration is also finding it difficult to get ahead of the virus.
Hundreds of federal scientists and health workers, including vaccine and food safety experts, have been laid off by the Trump Administration. Some may be rehired.
The CDC declined to answer 60 Minutes' questions, saying only it continues to respond to H5N1.
Colorado vet Russo – and others – told 60 Minutes they feel stymied: the current distrust of science and vaccines is hurting their fight to try to prevent the next pandemic.
"I would scorch the earth if this ends up in children deaths," Russo said. "And so as a mother, as a veterinarian, as a scientist, I'm just asking you: trust us, because I will do everything in my power and there's plenty of folks behind me that will do the same, to keep this from getting to that point."
