Avian influenza has scared doctors and scientists for a generation. But its arrival in the United States might finally give the H5N1 bird flu virus the combination of factors it needs to cause a global pandemic.
Those factors include a new carrier; dairy cattle; a regulatory system that protects farmers at the expense of human health; and a government bent on taking down an already weak public health infrastructure.
The H5N1 avian influenza virus making headlines around the world — and driving up the price of eggs — in the United States is no youngster. It’s been around since at least 1996, when it was first spotted in a flock of geese in Guangdong in southern China.
Since then it has spread around the entire world, tearing through flocks of poultry in Asia, Europe and the Americas and wiping out birds and mammals on every continent, including Antarctica. H5N1 bird flu only rarely infects people but as of the end of January 2025, the World Health Organization reported 964 human cases globally and 466 deaths, although many milder cases are likely to have been missed.
Vets and virus experts have had their eyes on H5N1, in particular, for decades. It didn’t look like a serious threat when it killed geese in 1996. But the next year the virus caused an outbreak in people just over the border from Guangdong in Hong Kong.
It infected 18 people and killed six of them before it was stopped. That got people’s attention. A 30% fatality rate is exceptionally high for a virus — something approaching the mortality of smallpox.
Mutations and swap meets
The virus gets its name from two prominent structures: the hemagglutinin, or H designation, and the neuraminidase, or N. All influenza A viruses get an HxNx name. The current circulating viruses causing human flu misery right now are H1N1 and H3N2, for example, as well as influenza B, which doesn’t get any fancy name.
But influenza viruses are exceptionally mutation-prone, and even the extra designation doesn’t tell the whole story about the changes the virus has undergone. Every time a flu virus replicates itself, it can make a mistake and change a little. This is called antigenic shift. As if this wasn’t enough, flu viruses can also meet up inside an animal and swap large chunks of genetic material.
The result? The H5N1 viruses now circulating are very different from those that were seen back in 1996 and 1997, even though they have the same name.
This is what’s been going on over the past 30 years. H5N1 has been cooking along merrily in birds around the world. So, after the 1997 outbreak, not much was seen of H5N1 until 2003, when it caused widespread outbreaks in poultry in China. Researchers discovered it could infect wild waterfowl without making them sick, but it made chickens very sick, very fast. And those sick chickens could infect people.
The best way to control its spread among poultry was to cull entire flocks, but if people doing the culling didn’t take the right precautions, they could get infected, and the virus caused serious, often fatal infections. Doctors began to worry that the virus would infect pigs. Pigs are often farmed alongside chickens and ducks, and they’re a traditional “mixing vessel” for flu viruses. If a pig catches an avian flu virus, it can evolve inside the animal to adapt more easily to mammals such as humans. Pigs have been the source of more than one influenza pandemic.
Pandemic planning
In the early 2000s, scientists and public health officials took H5N1 so seriously that they held pandemic exercises based on the premise that H5N1 would cause a full-blown pandemic. (Journalists were included in some of these exercises, and I took part in a few.)
But it didn’t cause a pandemic. Vaccines were developed and stockpiled. Pandemic plans were eventually discarded, ironically just ahead of the Covid pandemic.
However, flu viruses are best known for their confounding behavior, and H5N1 has always been full of surprises. It has evolved as it has spread, sometimes popping up and sometimes disappearing, but never causing the feared human pandemic. It has not spread widely among pigs although it has occasionally infected people around the world, as well as pet cats, zoo animals, wild seals, polar bears, many different species of birds and, most lately, dairy cattle.
It’s this development that might finally be a turning point for H5N1.
For a virus to start a human pandemic, it must acquire the ability to infect people easily; it must then pass easily from person to person; and it must cause significant illness.
Competing interests
So far, this hasn’t happened with H5N1. It has infected 68 people in the United States, mostly poultry or dairy workers. Mostly, it causes an eye infection called conjunctivitis, although it killed one Louisiana man. But it is spreading in a never-before-seen way — on milking equipment and in the raw milk of the infected cattle.
“The more it spreads within mammals, that gives it more chances to mutate,” said Nita Madhav, a former U.S. Centers for Disease Control and Prevention researcher who is now senior director of epidemiology and modeling at Ginkgo Biosecurity. I interviewed her for a podcast for One World One Health Trust. “As it mutates, as it changes, there is a greater chance it can infect humans. If it gains the ability to spread efficiently from person to person, then it would be hard to stop,” Madhav said.
And while some states are working to detect and control its spread, the federal government is not doing as much as public health experts say it should. Two agencies are involved: the U.S. Department of Agriculture (USDA) and the Centers for Disease Control (CDC).
Dr. John Swartzberg, a health sciences clinical professor emeritus at the University of California, Berkeley said in an interview with the UC Berkeley School of Public Health that the USDA is charged with two responsibilities that only sometimes work in concert.
“One of the responsibilities they have is to assure a healthy agricultural industry for the United States,” Swartzberg said. “The second responsibility is to assure safety of the human beings who consume agricultural products in the United States.”
More information, not less, is needed.
Dairy farmers feared they’d lose money if their farms were identified as sources of infection. And it’s a lot more expensive to cull cattle than it is to cull chickens.
“And I think what we’ve seen with this bird flu problem is that the USDA is tilted in favor of protecting the industry, as opposed to protecting the health of humans,” Swartzberg said. “CDC is also involved, but the CDC has no authority to go into states and tell them what to do. It has to be done state by state.”
On top of that, U.S. President Donald Trump has ordered the CDC to take down websites reporting on avian flu and other issues. He is withdrawing U.S. membership from WHO, crippling the ability to coordinate with other countries on controlling outbreaks of disease.
He notably tried to suppress reporting about Covid during his previous presidency and promoted unproven and disproven treatments.
His newly confirmed Health and Human Services Secretary, who will oversee CDC and other agencies charged with human health, Robert F. Kennedy, Jr, is a vaccine denier, proponent of raw milk and has no public health qualifications.
The stubbornness of people in the United States doesn’t help. When public health officials warned against drinking raw milk last year, raw milk sales actually went up.
“Food safety experts like me are just simply left shaking their heads,” Donald Schaffner, a Rutgers University food science professor, told PBS News.
The big fear? That in flu season, someone will catch both seasonal flu and H5N1, giving the viruses a chance to make friends in the body, swap genetic material and make a deadly new virus that can infect people easily.
Three questions to consider:
1. How can politics affect public health risk?
2. How does public understanding and trust affect the risk of disease?
3. Countries often blame one another for the spread of disease, but should they?
