Could Avian Flu Cause Our Next Pandemic?

Colleagues, it’s time to wake up and smell the coffee. Or, for a true reality check, just scan the Department of Agriculture’s frequently-updated map and tables naming the many animals that have tested positive for highly pathogenic avian influenza (HPAI) in the U.S. since May 2022.

Finding influenza A/H5N1 in wild birds and waterfowl and poultry is nothing new, of course. During 2024, however, our country has seen its first-ever multi-state outbreak in dairy cows expressing milk heavily tainted with the virus, as well as illness, deaths, or detections in cats, goats, alpaca, skunks, and house mice, among others. The latest species found to harbor A/H5N1 was a backyard pig in Oregon. Once euthanized, its tissues teeming with virus fueled further unease because pigs are classic mixing vessels in which human and avian flu viruses can recombine and form new, virulent strains.

Now for some less ominous news: the viral strain currently circulating in American dairy cows and poultry has not yet caused serious disease in people. Thus far, based on very limited testing, roughly four dozen A/H5N1 infections almost equally divided between dairy and poultry workers have been mild or even asymptomatic. As a result, CDC continues to state that the risk to the general public is low.

Having said that, there is now a critically ill teenager up in Canada infected with H5N1 whose source of exposure is unknown. In addition, no knowledgeable expert would deny that influenza viruses are notoriously unpredictable, having caused more pandemics than any other pathogen over the last 500 years. Now factor in the modern challenge of getting Big Agriculture, government, and public health to work hand-in-hand on control measures while communicating clear, sensible advice to everyday folks already exhausted by COVID, a few of whom also believe that raw milk is Nature’s perfect food, discounting its previously proven hazards as mere hogwash.

So, just for a moment, imagine that A/H5N1 further evolves in 2025, leading to far more numerous and harmful infections in humans. If that happens, how will history judge our country’s political will and ground-level efforts to prevent this disaster? A day late and a dollar short? Or how about downright inept (to echo one global expert’s reaction)? Most importantly, going forward, what proactive measures and messages could still curb HPAI’s growing risk of animal-to-human spread?

A Noted Expert Weighs In

In late October, the National Academies of Science convened a 2-day virtual public workshop entitled “Potential Research Priorities to Inform Readiness and Response to Highly Pathogenic Avian Influenza A (H5N1).” Shortly before the event, Stephen Ostroff, MD — a highly-respected public health expert who formerly worked at both CDC and FDA (at FDA, Ostroff was, at different times, the agency’s chief scientist and acting commissioner) — was asked to attend and comment on possible gaps in a future research agenda.

After listening to a full day of “very smart” talks, Ostroff weighed in with a key observation — namely, that one glaring gap was a plan for systematic research on reasons why people might be reticent to follow government recommendations on issues ranging from farming practices and the interstate movement of potentially-infected animals to environmental surveillance and diagnostic, therapeutic, and preventive interventions for animals and humans.

“It’s great to develop diagnostics, therapeutics, and vaccines,” he later told me, “but the problem is: it’s kind of like the ‘Field of Dreams’ phenomenon. And that’s the analogy I used, which is — just as during COVID — there was this implicit assumption that ‘If you build it, they will come.’ What happens if they don’t come?”

Ostroff also highlighted other overlooked questions: for example, could previously-sick cows get re-infected with A/H5N1? And what about household pets’ potential role in transmitting the virus to humans?

“Given what we’ve already seen in some of these farms where barn cats drink the milk and end up with aggressive illness and a 50% fatality rate, I specifically mentioned: if people like to drink raw milk…the pets in their house probably drink it too.”

Finally, what if a cow with asymptomatic A/H5N1 infection went to slaughter? As Ostroff reminded me, certain people also feed raw-beef products to their pets. In fact, while at FDA, he sometimes oversaw national recalls after Salmonella or another bacterial pathogen contaminating such products sickened not just a pet but humans in the same household. In 2025, ingesting raw milk, beef, or chicken could be one more way a pet could get sick, shed A/H5N1 virus in its respiratory secretions or stool, and thus expose its owner.

More Pertinent Facts and Prescriptions

Not long ago, I visited the website of a leading raw-milk purveyor here in California. That’s right: My home state is one of many in the U.S. where it’s currently legal to sell raw milk to humans.

In light of this year’s bovine outbreaks now affecting 278 dairies in Central California, I expected the homepage to at least contain a warning about HPAI. But here’s what I found instead: a pop-up banner stating “NEW PET FOOD, FROZEN RAW MILK — NOW AVAILABLE NATIONWIDE.”

What?

After mentioning this to Ostroff, the veteran regulator confirmed a relevant fact: Although FDA prohibits the interstate sale of raw milk for human consumption, that’s not the case for raw milk meant for animals. At the same time, he added, “Even though the websites read [frozen raw milk] for pets, it’s sometimes essentially a ‘wink, wink, nod, nod’ way to sell raw milk to people without having to adhere to state and federal requirements.”

And just to be clear: although pasteurization kills A/H5N1, freezing does not. In Ostroff’s words: “Viruses like to be frozen.”

Finally, Ostroff and I discussed an important breakthrough that may offer hope to some and stir fear and mistrust in others: new vaccines, both for cows and people, designed to protect them against A/H5N1. If Ostroff had his druthers, the A/H5N1 component would eventually be added to our standard yearly flu shot.

But no, we have not yet reached a moment when experts are recommending that humans be vaccinated against HPAI. Having said that, if and when that time comes, dairy and poultry workers — many of whom are immigrants — will be a key group to target.

My final concern? At that point, will those high-risk individuals’ employers, agribusiness, government, public health leaders, and civil society have finally reached a consensus on a full suite of measures to forestall a pandemic? For now, we can only hope.

For more information about the best ways to protect yourself and counsel patients on avoiding infection with highly pathogenic avian flu, visit CDC’s website.