These days, when someone comes to do chores at the Moline Brothers turkey farm in northwest Iowa, they park in a designated lot at the edge of the property. They enter a small building with a single purpose: to cache everything that they brought onto the farm from the outside world. They change into clothes and boots that are reserved for them, exit the far side, get into a farm-owned truck, and drive to the barn where they’ll be working. At the barn, they pull on coveralls, swap boots again, and swish their feet through a tub of disinfectant before they enter the long, sunny building full of cheeping baby poults.

It’s a burden, more than the Molines—Brad, Grant, and their father, John—have ever asked of their employees before. So is telling the guy who drives the single feed truck they allow on the property not to get out of his truck’s cab, and unhooking the bin lids and guiding the long delivery tube themselves. And so is going down the road to another address to fetch UPS and FedEx packages that normally might come to their door. Deliveries aren’t allowed on the farm any more.

Each of those maneuvers shares a single objective: keeping avian influenza away from their birds. The Molines have intimate experience with the virus. When bird flu tore through the Midwest in 2015, creating the largest animal-disease disaster in US history, they lost hundreds of turkeys to the disease overnight and were required to have their entire flock of 56,000 slaughtered. Afterward, they built new barns, imposed new work rules, and tuned up their farm’s defenses. Now, with the pathogen advancing across the US in amounts not seen since 2015, the Molines are strengthening their biosecurity to the highest levels they can manage as independent farmers, and hoping to stave off another disaster.

“Everyone has worked with us really well, because they all went through 2015 too,” Brad Moline said Friday morning, raising his voice over the musical gargling of 4-week-old turkeys burbling around his ankles. “We’re all in this together. No one wants to see that happen again.”

It’s hard to take stock of this, being still in the midst of Covid, but the US is in the grip of a ferocious epidemic—a panzootic, in technical terms—caused by highly pathogenic avian flu. So far, there has been no threat to human health, though bird flu strains have jumped species to sicken humans before. But the harm to farmers and the food supply is already profound; as of Friday, more than 27 million birds, including almost 5 percent of all egg-laying hens in the country, had died or been killed to slow down its spread.

The onslaught is forcing reevaluation of the possibility of vaccinating US poultry against the disease, a step that parts of the poultry industry and also federal policymakers have rejected for years. But while vaccines are used in other nations, there are none in routine use in the US that could stop this wave—and even if one were used, it could not stop a parallel wave of the same flu that is ripping through wild bird species in an unprecedented way.

As of last week, the fast-moving pathogen had been found in poultry and adjacent species 182 times in 27 states, according to the Animal and Plant Health Inspection Service of the US Department of Agriculture. It has invaded every type of bird-growing operation—turkeys, broilers, egg-laying farms, and breeders that produce eggs for hatching—as well as backyard flocks, pet chickens, and game birds bred to be released for shooting.

Simultaneously, the flu has been found 665 times in 32 states in wild birds, both among birds that are hunted, such as mallards and widgeons, and in charismatic predators, such as snowy owls and bald eagles, in which it is almost 100 percent fatal. Last week, in a post that sent ripples of sadness across social media, the University of Minnesota’s Raptor Center announced it had to humanely euthanize a sick family of great horned owls—a mated pair and three fuzzy babies—that were nesting in a downtown park.

It is an extraordinary wave of illness given that highly pathogenic avian flu was only identified in the US in January, in three ducks shot by hunters in North and South Carolina; the virus was detected after the ducks were checked by wildlife biologists doing routine surveillance. But it parallels its extreme spread in Europe and the Middle East last winter and this year. There were vast die-offs of cranes in Israel, ducks in France, and geese in the United Kingdom, along with millions of poultry in the Netherlands, the Czech Republic, and Germany. In Canada, only one province, Manitoba, remains free of avian flu.

The interplay between the disease in wild birds and in commercially raised ones is complex. In 2015, farm birds sometimes became infected by viruses that crept in from other farms, either on contaminated shoes and tires, or through plumes of pathogens drifting on the wind. This year, every farm infection appears to have come from wild-bird contact, says Yuko Sato, a poultry veterinarian and assistant professor at the Iowa State University College of Veterinary Medicine. “The industry has refined how it responds since 2015,” she says. “If we have somewhere that tests positive, the priority is to put down those birds as soon as possible, because the longer they stay on the site alive, the viral load is just going to keep ramping up. So farm workers are getting better at noticing when something in their flock is off.”

A subtlety of so many types of farms experiencing outbreaks is that each type of bird—breeders, broilers, turkeys, layers—is raised in a different type of housing, which means there cannot be a single design flaw among all of these facilities that has allowed the virus access. The vulnerability may be more simple: their location. Farms are in the countryside, under the flyover paths of wild birds—and near roosting sites, if there are ponds or attractive food nearby. Bird poop containing the virus could wind up in the grass on a farm, or on rodents that have moved through the grass, or on stubble that blows off nearby fields, or in smaller birds, such as swallows, that have contact with migrating birds. Or it could be in all of these, which means even a small lapse in farm safety procedures could let the virus in.

The 360-degree nature of the threat could lead the US poultry industry to accept vaccination for the first time. Before, vaccination has always been ruled out because it prevents disease, but not infection, meaning that vaccinated birds could spread the virus undetected. (If this sounds like questions that were raised over Covid vaccines: Yes, it’s the same problem.) That possibility seemed not worth the risk to US producers, especially because other countries that are free of bird flu might turn away US chicken as a disease-importation risk. With bird flu so widespread now, that attitude may be changing. The US Department of Agriculture is supporting research projects to develop vaccines for the particular strains of flu that are most destructive in chickens. One, based at the University of Minnesota, recently escalated its testing from lab work to mice.

A vaccine that works immunologically would still face practical hurdles, such as the cost to farmers, the difficulty of administration, and working out dosing and timing. It would also need to be tuned to the particular strains affecting birds; just as for humans, there is no universal flu vaccine. Farmers and the industry would have to decide whether there are subsets of the vast US poultry flock that would most benefit from vaccination. Those might be birds in the near vicinity of an outbreak; or species whose production cycle lets them live longer, such as turkeys compared to broilers; or birds of particular economic value, such as breeder hens that are repositories of proprietary genetics. Or all of them. It is not something that could be put in place quickly.

“Before 2015, we had not considered this, and so we hadn’t developed ways to do it. And now we are playing catch-up,” says Carol Cardona, a wildlife veterinarian and chair of avian health at the University of Minnesota College of Veterinary Medicine. “You can see how long it took to put Covid vaccination in place, and that was for one species, humans. And we had all the technology in place already. We don't have the technology in place to do this right now.”

There’s a further complication to rolling out a poultry flu shot in the US. While some vaccine formulas have long-standing approval here, they have not been used in decades. In the enormous 2015 outbreak, the USDA evaluated them against the avian flu strain rolling across the country and decided none of the formulas were effective enough, or a close enough genetic match, to justify the cost of ramping up production and the time to get any vaccine out to the field. Some other countries routinely vaccinate poultry, but those initiatives have not all been success stories. In Egypt, for instance, birds developed diminished immune responses to the vaccine. Instead of chasing the virus from the Egyptian flock, that allowed the disease to become endemic there—making it not an episodic threat but a permanent one, to humans as well as to poultry.

Turning avian flu into an endemic disease could create a permanent threat to wild birds also. Wildlife biologists uneasily acknowledge that something is different this year. Flu’s point of intersection between the wild world and domesticated birds was always thought to be among ducks and other waterfowl, which can carry the virus without being sickened by it. If other wild species fell ill—a raptor after eating a duck, for instance—those cases were considered rare. But this flu is already hitting wild birds hard. “We've had thousands of birds die in Florida; we have ongoing outbreaks in black vultures,” says David Stallknecht, a wildlife epidemiologist and director of the Southeastern Cooperative Wildlife Disease Study, a research institute housed at the University of Georgia. “We've had 20 positive eagles from Florida, South Carolina, Georgia, and North Carolina alone. Snow geese in the Midwest, they probably have thousands dying.”

Since wild birds cannot be inoculated, the only hope is that viruses spreading among them burn themselves out. And since there is no vaccine yet, farmers such as Brad Moline must remain on guard. Early last week, tornado-force winds damaged farms not far from him and sent dust swirling across the landscape, from the direction of lagoons where snow geese had roosted earlier this spring. He was contemplating layering landscape cloth over his barns’ ventilation outlets to keep out possible contamination, just to be sure.

Vaccinating every bird on the farm against every flu outbreak might not be necessary, he said. But he could envision vaccinating birds that are growing during the spring migration season. His turkeys already get a half-dozen vaccines to protect them against other diseases, and this would be no different. “I’m a huge advocate of vaccines,” he says. “I think we would have to seriously look at this, the way this thing's blowing up worldwide.”

• 📩 The latest on tech, science, and more: Get our newsletters!
• The race to rebuild the world's coral reefs
• Is there an optimal driving speed that saves gas?
• As Russia plots its next move, an AI listens
• How to learn sign language online
• NFTs are a privacy and security nightmare
• 👁️ Explore AI like never before with our new database
• 🏃🏽‍♀️ Want the best tools to get healthy? Check out our Gear team’s picks for the best fitness trackers, running gear (including shoes and socks), and best headphones