Since early 2022, a highly pathogenic strain of avian influenza has been decimating wild bird populations and wreaking havoc on North American poultry farms (you’ve probably noticed the resulting rise in egg prices). In the past year, this strain of H5N1 has also been detected in mammals ranging from raccoons to seals and—for the first time ever in the U.S.—people.
Not wanting to trigger a panic—or get caught unprepared for the next pandemic—scientists, government agencies, and an army of experts in human and animal health are monitoring the virus’s spread and hoping it doesn’t mutate enough to gain a foothold in humans.
Should you worry? Not just yet. Here’s what you need to know.
How bad is the outbreak?
The current wave of H5N1 avian flu—an influenza type A virus that first emerged in Chinese poultry in 1996 and has been circulating worldwide ever since—arrived in North America in December 2021. (The last major outbreak here was in 2014 and 2015.) Within a year, wild bird outbreaks were confirmed in 47 U.S. states.
According to the Centers for Disease Control and Prevention, since the start of the latest outbreak nearly 59 million domestic poultry have died from the virus or been culled to stop its spread. More than 58 million birds have died or been culled at H5N1-affected poultry farms in 37 European countries since October 2021. The virus has also been detected in 16 countries in Latin America and the Caribbean. The World Organisation for Animal Health estimates that more than 50,000 wild birds have died of H5N1 since October 2021 (likely a significant undercount), including a massive die-off of at least 5,500 pelicans in Peru last fall.
Is it still spreading?
Yes. Wild birds appear to be the major route of transmission, spreading it to domestic poultry and “backyard” hobby birds along their migration routes. (Ducks and geese are on the move right now.)
“Wild waterfowl are the natural reservoirs for avian influenza viruses and typically do not get sick from the virus but can transmit it to domesticated poultry with disastrous results,” says Jarra Jagne, an associate professor and poultry veterinarian at Cornell University College of Veterinary Medicine. The Animal and Plant Health Inspection Service (APHIS) of the Department of Agriculture runs a wild bird surveillance program that monitors populations for avian influenza viruses of concern in the U.S. In the past week or so alone, it has confirmed cases of H5N1 in wild geese, ducks, crows, owls, and eagles in all parts of the country.
Can we vaccinate poultry?
While new rules that went into effect March 12 cleared the way for vaccination of poultry in Europe, easing restrictions on the movement of vaccinated animals and their products, the government agency responsible for animal health in the U.S. (USDA-APHIS) has not authorized the use of vaccination as a control measure here. There are several avian influenza vaccines that are licensed by the APHIS Center for Veterinary Biologics, but Jagne says their efficacy against the prevailing strain is not known.
“Vaccinating for avian influenza viruses is a complex undertaking that includes a myriad of issues. Avian influenza viruses change frequently, making vaccines obsolete in a very short time,” Jagne explains. “Vaccination does not stop birds from getting infected with the virus but only reduces or eliminates clinical signs.”
Veterinary vaccines can take years to get approval, though there are potential shortcuts. But a major factor in deciding whether to vaccinate poultry is trade: “Countries that trade with the U.S. will not accept poultry products from vaccinated animals because available laboratory tests cannot distinguish vaccine viruses from wild-type viruses,” Jagne says. That would be a big problem for the $6 billion poultry export industry.
Is it just birds?
No. The USDA’s National Wildlife Disease Program has detected H5N1 in mammals, including mountain lions, bobcats, foxes, skunks, bears, raccoons, otters, and seals. Last summer, more than 150 dead or ailing seals infected with H5N1 transmitted by seabirds washed up on beaches in Maine. And an outbreak of H5N1 at mink farms in Spain in October 2022 raised new concerns that variants of the virus better adapted to mammalian airways could emerge through an intermediate mammal species.
Can people get it?
Yes. Avian flu has a 50% mortality rate in humans, but avian flu doesn’t jump over to humans very often—and human infections have occurred most often in people who have had close contact with infected birds or surfaces contaminated with bird flu viruses. Worldwide, since 2003 there have been 873 human cases of H5N1 and 458 deaths reported in 21 countries, according to the World Health Organization.
The first known human case of the highly pathogenic H5N1 in the U.S. was reported in April 2022 in a person who worked culling infected birds at a farm in Colorado. The patient was isolated, and recovered after being treated with antivirals. In Cambodia this February, an 11-year-old girl died from H5N1, and her father was infected with the virus as well. But Cambodian authorities confirmed that both contracted the virus from contact with poultry in their village, and that there was no human-to-human transmission of bird flu. Also, both father and daughter were infected with a different clade, or lineage, of the virus than the one that is widely circulating here.
Is this the next pandemic?
It’s not impossible, but so far the spread of avian flu from one infected person to close contacts is very rare, and when it has happened, it has spread to only a few people. Experts say we’re unlikely to see widespread transmission of H5N1 among people unless some sort of mutation occurs that helps it bind to a receptor found on cells in the nose and upper airway of humans. That said, as more infections occur in mammals there are more opportunities for the virus to evolve, which is why the WHO and research partners around the world are monitoring mutations closely.
How do you know if you have it?
Bird flu symptoms are similar to common flu symptoms: fever, muscle aches, congestion, cough, and shortness of breath. But infection can’t be diagnosed by clinical signs and symptoms alone. If you’ve had exposure to sick birds, you need to get tested—with a nasal swab routine that you’re probably all too familiar with. CDC influenza tests, which can detect both seasonal and novel influenza A viruses, such as H5N1, are used in all 50 U.S states and globally. There are also CDC tests available in public health labs in all 50 U.S. states and internationally that specifically detect the current H5 viruses.
“If you get sick, antiviral drugs such as Tamiflu have been used successfully to treat avian influenza infections in humans,” Jagne says. The CDC also recommends getting a seasonal flu vaccine, which may reduce symptoms.
Is there a vaccine?
The CDC has produced an H5 candidate vaccine virus, or CVV—a sort of template to make a vaccine—that is identical or nearly identical to the virus found recently in birds and mammals. The CVV is available and has been shared with vaccine manufacturers. An inactivated vaccine for H5N1, called Audenz, is already FDA-approved and manufactured by Seqirus Inc. And drug maker Moderna, which has developed mRNA vaccines for COVID-19, says that it plans to advance to clinic trials with an mRNA vaccine for bird flu.
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