How Serious Is the Worst Bird Flu Outbreak in U.S. History?

Some lawmakers are warming to the idea of a vaccination campaign, long considered a fringe idea due to the cost and potential consequences. Trade groups warn that vaccinated poultry would not be accepted in many overseas markets, disrupting exports.

While bird flu likely poses little health danger to humans, it’s contributed to spikes in U.S. egg prices and decimated poultry flocks. Among the domestic poultry affected are chickens, turkeys, pheasants, quail, ducks and geese — in both big commercial operations and increasingly popular backyard flocks.

Since the current strain of highly-pathogenic avian influenza — H5N1 — began circulating in the country in February 2022, farmers across the country have lost or had to cull more than 58 million poultry birds. 

The USDA estimates it has already spent more than $670 million in insurance indemnities and sanitation services to combat the ongoing bird flu outbreak.

And with many wild birds starting their spring migration, roughly 140,000 poultry birds were infected with the virus nationwide in April.

While food costs are stabilizing, members of Congress from both parties are asking how the U.S. can do better at controlling bird flu.

“We’ve all seen first-hand how high pathogenic avian flu has devastated domestic poultry populations, where depopulations have had to take place,” said Rep. Jim Costa, a California Democrat, at an April 18 House Agriculture Committee hearing.

“We’ve got to continue to refine and improve our approach to address animal disease, and USDA needs all the tools to guarantee a robust response.”

The USDA is testing two proprietary vaccines developed through its Agricultural Research Service, as well as bird flu vaccines from pharmaceutical companies Merck Animal Health and Zoetis, Inc.

But animal health experts note that a bird flu vaccine is not the immediate solution that some believe it to be.

Jenny Lester Moffitt, undersecretary for marketing and regulatory programs at the USDA, said at an April 24 press event that it will take a minimum of 18 to 24 months to produce a viable vaccine, which is not guaranteed to be effective against infection.

Yuko Sato, a poultry veterinarian and associate professor at Iowa State University in Ames, Iowa, said at an April 26 media event that “the vaccine is not a silver bullet” for an end to the outbreak.

“You would have to make sure that if you vaccinate — but still have positive birds — you can stamp out the virus,” Sato said. “Otherwise, we’ll never be looking at eradicating the virus from the United States.”

Here are the answers to some common questions about the ongoing bird flu outbreak and potential vaccines:

What is highly-pathogenic avian influenza?

Highly-pathogenic avian influenza, commonly known as HPAI, bird flu, or “high-path,” is a deadly respiratory virus that affects wild birds and poultry.

The contagious disease comes from the Influenza A family, and is characterized by the H5 or H7 categories of hemagglutinin — or spike protein — structures on its surface, which it uses to infect cells. The virus is spread via airborne transmission, or exposure to the byproducts of an infected bird, like saliva, mucus or feces.

Poultry and other domesticated birds with the disease will often exhibit a lack of energy, produce soft-shelled or misshapen eggs, and have swollen heads.

The highly-pathogenic version of the disease was first identified in China in 1996, and has mutated several times over the last three decades through swapping genetic material with low-pathogenic avian influenza strains within wild birds.

David Swayne, former director of the Agricultural Research Service’s Southeast Poultry Research Lab in Athens, Georgia, said at an April 26 media briefing that 87% of avian influenza strains are made up of blended genetic material from other strains. He said that this natural mutation process can make a vaccine less effective against the virus year over year.

Wild migratory birds are the primary transmission vector in the current outbreak, accounting for roughly 85% of disease spread, according to the USDA. These animals, including terns, ducks, and geese, can contract and pass along the disease without obvious physical symptoms.

Yet an HPAI infection spreads quickly among a flock of poultry, with infections leading to mortality at a rate of 90% to 100% in chickens and turkeys, often within 48 hours, according to the Animal and Plant Health Inspection Service.

When a farmer detects the disease in a commercial flock, the only USDA-recommended option is to kill the remaining birds, dispose of the carcasses, and decontaminate the facility to mitigate spread.

Who is getting infected? Should I be worried?

Despite the threat H5N1 presents to poultry, experts with the Centers for Disease Control and Prevention say that people do not need to brood over getting sick.

The agency reports that 11 cases of bird flu have been reported among humans since 2021, with only one “mild” case occurring in the United States. And as of 2023, there have been no reported cases of human-to-human transmission of HPAI, according to the World Health Organization. 

Swayne said at the media event that only 875 human cases of H5 bird flu have been reported since 1996. About 40% were fatal. He noted these infections have occurred largely among humans handling domesticated poultry, and not from encounters with wild birds.

The USDA has documented 176 mammals in the United States  infected with the disease since 2022, including skunks, foxes, seals, and mountain lions, among other species. Wildlife experts from the U.S. Geological Survey published a study in April finding much of this disease spillover can be traced back to predation on wild birds.

Still both Swayne and Hill pointed to a recent event in which 3,500 sea lions became infected with the virus in Peru as one worth monitoring for mutations that could affect mammals.

How does the current outbreak compare to past bird flu outbreaks?

The current iteration of the highly-pathogenic avian influenza virus was first detected domestically on January 13, 2022, in a wild bird in Colleton County, South Carolina. The first domesticated animal case of the disease was found on a turkey farm in Dubois County, Indiana on February 8, 2022.

Since then, the disease has spread across 47 states, affecting more than 833 commercial and backyard poultry flocks.

Still, this is not the first outbreak of HPAI that the federal government has responded to. And despite the scope of these numbers, many animal health experts say current USDA efforts represent a significant improvement over earlier outbreaks of the disease.

Sato recalled that a 2015 outbreak of HPAI, previously considered the worst outbreak on record, required the culling of 50.4 million birds on Midwestern poultry operations.

She added that 70% of the cause of new infections from that outbreak was farm-to-farm lateral spread from workers in 21 states, including Arkansas, Iowa, Idaho, Indiana, Kansas, Kentucky, Michigan, Minnesota, Missouri, Montana, Nebraska, New Mexico, Nevada, Oregon, South Dakota, and Wisconsin.

In contrast to that outbreak, Sato said that now “we’ve done a really good job with biosecurity.” Biosecurity refers to preventive measures producers can take to limit spread of the disease, like disinfecting farm machinery and providing clean clothing and protective equipment to farmworkers.

Sato said that with producers embracing these practices, the lateral spread of avian influenza decreased from 70% of reported cases in 2015 to roughly 16% of reported cases in 2023. 

Moffitt added that efforts to control the virus are projected to cost the country less than 50% of its 2015 expenditures of $1.6 billion.

However, animal disease experts caution that the U.S. is dealing with a more widely dispersed and distinct disease than that of the 2015 HPAI outbreak.

Nichola Hill, an assistant professor of biology at the University of Massachusetts, said at the April 26 media event that researchers have detected the virus in 150 of the approximately 1,000 wild bird species found in the U.S., and the disease has affected more than 6,000 wild birds. 

Greg Tyler, the president and CEO of USA Poultry and Egg Export Council, said that this version of the disease has also gotten into all four major migratory flyways for wild birds in the U.S.

Sato said that more backyard flocks of poultry are being affected by the spread of bird flu from migratory populations — a total of 507 small to mid-sized flocks — in contrast to the 21 backyard flocks affected in 2015.

There are also new concerns emerging among experts that this deadly disease could become endemic to North America without significant public-private collaboration to reduce spread, according to an April study from researchers at the University of Maryland.

“Federal agencies, state agencies, the agriculture sector and wildlife management — we are all going to have to deal with this together, because we can’t afford not to,” said Jennifer Mullinax, an assistant professor in the University of Maryland Department of Environmental Science and Technology, in a release. 

What about a vaccine?

While some animal health experts say developing a vaccine for the current bird flu strain could be a valuable tool, trade experts caution that a national vaccination strategy would not come quickly, or without tradeoffs for the nation’s $6 billion poultry export industry. 

Sato said that a national vaccination strategy for the roughly 10 billion commercial-purpose birds in the United States could be time-intensive, and cost billions of taxpayer dollars.

Tom Super, senior vice president of communications at the National Chicken Council, said that his organization does not support the use of a vaccine for HPAI right now, as most countries do not accept exports from countries that vaccinate for the virus.

These non-tariff trade barriers are designed to protect other nations’ unvaccinated poultry flocks from immunized birds that still carry the disease. Super added that if the U.S. vaccinates domestic birds, the broiler industry will be cut off from exports, costing billions of dollars to the U.S. economy every year.

Tyler added that his organization found that if a vaccination campaign happens without adjustments to trade policy, there could be a potential loss of 200,000 farm jobs.

Moffitt said that negotiations between the USDA and foreign partners are still ongoing to maintain international poultry export markets for certain states amid outbreaks in others in the country.

Tyler said that the Department of Agriculture’s Animal and Plant Health Inspection Service and Foreign Agricultural Service have made significant progress in developing regionalization agreements with foreign governments since 2015.

He noted that the U.S. poultry industry has managed roughly $11.7 billion in exports over the last two years, despite the ongoing challenges of HPAI and bans on poultry exports by certain countries like China.

Super and Tyler both advocated for continued funding for the Animal and Plant Health Inspection Service to provide rapid-response support to farms.

Moffitt urged adhering to biosecurity measures like interstate surveillance and the Defend the Flock program at the April 18 hearing. Moffitt cited that the number of infections in commercial flocks in March 2023 decreased tenfold compared to March 2022, proof the USDA’s current strategy of rapid tests and reporting is working.

“We know how to respond quickly, so producers can get back to producing food, how important biosecurity is, how to keep markets open,” she said. “We know what to do, and we are ready.”