Bird flu in humans is an infection caused by avian influenza viruses that normally circulate in wild birds and poultry but occasionally jump to people. These infections are rare, but they can be severe. Globally, 954 confirmed human cases of the most well-known strain, H5N1, were reported between 2003 and late 2024, and nearly half were fatal. In the United States, a wave of cases tied to dairy cattle outbreaks has brought renewed attention to the virus, with 71 confirmed human cases as of 2025.
How People Get Infected
Bird flu viruses reach humans through close contact with infected animals or contaminated environments. The most common route is touching infected birds or other animals during handling, slaughtering, or processing, then touching your eyes, nose, or mouth. The virus is present in an infected animal’s respiratory droplets, saliva, mucus, and feces, so even indirect contact with contaminated surfaces can be enough.
Airborne transmission is also possible. Dust particles and tiny droplets containing the virus can be expelled into the air around infected animals, and a person nearby can inhale them. The closer you are to the animal or contaminated space, the higher the risk. In the current U.S. outbreak, 41 of the 71 confirmed cases were linked to exposure on dairy farms, where workers come into close contact with infected cattle and the environments around them.
Drinking or eating something contaminated with live virus, such as raw (unpasteurized) milk from an infected cow, is another possible route. Properly cooked poultry and eggs do not carry this risk. There is no evidence that well-prepared food transmits H5N1 or other avian influenza viruses.
Person-to-Person Spread Remains Extremely Rare
The reason bird flu hasn’t triggered a pandemic is that it spreads very poorly between people. On rare occasions in other countries, limited person-to-person transmission has occurred, typically within families where someone provided prolonged, close care to a very sick relative without wearing protective equipment. These chains of spread have been short and have not sustained themselves in the general population.
For the virus to spread efficiently between people, it would need to acquire specific genetic mutations. Researchers at Scripps Research identified one key change, called Q226L, that significantly improves the virus’s ability to latch onto receptors found in human airway cells. But that alone wouldn’t be sufficient. Additional mutations that help the virus replicate more efficiently inside human cells would also likely be needed. Scientists monitor circulating strains closely for any sign these changes are accumulating.
Symptoms Range From Mild to Life-Threatening
Human bird flu infections don’t always look the same. The severity depends heavily on the viral strain and the amount of exposure. Some people, particularly those in the recent U.S. dairy farm outbreak, have experienced only mild symptoms like eye redness and irritation (conjunctivitis), sometimes with mild respiratory symptoms resembling a cold. Others have had typical flu-like illness: fever, cough, sore throat, and muscle aches.
At the severe end of the spectrum, H5N1 can cause viral pneumonia that progresses rapidly to respiratory failure and multi-organ damage. This is where the alarming fatality numbers come from. The global case fatality rate for H5N1 sits at roughly 49%, though this figure likely overstates the true death rate because mild cases often go undetected and unreported. Still, H5N1 is clearly capable of causing severe, life-threatening illness in ways that seasonal flu rarely does.
Which Strains Infect People
Several subtypes of avian influenza have crossed into humans. H5N1 is the most notorious, responsible for hundreds of cases across 24 countries since 2003 and for the first U.S. bird flu death, reported in Louisiana. H7N9, which emerged in China in 2013, caused a large wave of human infections before being brought under control through poultry vaccination. H5N6 has caused sporadic but often severe cases as well.
The strain currently circulating in U.S. livestock belongs to the H5N1 clade 2.3.4.4b lineage, which has spread widely in wild birds and crossed into dairy cattle, an unexpected host. This same lineage has been detected in poultry flocks and some wild mammals, expanding the number of potential exposure points for farmworkers and others in close contact with animals.
How It’s Diagnosed
If you develop symptoms after contact with potentially infected birds, poultry, or cattle, standard rapid flu tests from a pharmacy aren’t reliable for detecting bird flu. The WHO specifically recommends against using commercially available rapid tests for this purpose because their accuracy for avian strains is unknown, and they can’t distinguish between influenza subtypes.
Confirmation requires specialized laboratory testing, typically a type of molecular test called RT-PCR performed at a public health laboratory. Respiratory samples need to be collected quickly, and in some cases blood specimens are taken as well. If there’s any suspicion of human-to-human spread, samples are sent to designated reference laboratories for detailed genetic analysis of the virus.
Treatment Options
The same antiviral medications used for seasonal flu also work against bird flu strains. Most circulating H5N1, H7N9, and H5N6 viruses respond to neuraminidase inhibitors (the drug class that includes Tamiflu) and to baloxavir, a newer antiviral. Treatment works best when started as early as possible after symptoms begin, which is why rapid testing matters.
For people sick enough to be hospitalized, doctors sometimes use a combination of two different antiviral drugs because the virus can develop resistance to a single medication during treatment. Resistance to Tamiflu has been documented in hospitalized H5N1 patients, with fatal outcomes in some cases. The older class of flu antivirals, adamantanes, are essentially useless here since most avian influenza strains are resistant to them.
Who’s Most at Risk
The people most likely to encounter bird flu are those who work directly with animals: poultry farmworkers, dairy workers, veterinarians, and anyone involved in culling infected flocks. Backyard poultry owners, hunters who handle wild birds, and laboratory workers studying the virus also face elevated risk.
For these groups, protective equipment is the primary line of defense. Federal guidelines call for N95 respirators (properly fitted through a formal program), safety goggles that seal around the eyes, disposable gloves, fluid-resistant coveralls with waterproof aprons, disposable shoe covers or disinfectable boots, and head and hair coverings. The eye protection is particularly important given how many recent cases have involved conjunctivitis, suggesting the eyes are a significant entry point for the virus.
Vaccines in Development
There is no widely available bird flu vaccine for the general public, but development is well underway. Multiple companies are testing next-generation H5 vaccines using mRNA technology, the same platform behind COVID-19 vaccines. Moderna’s candidate is the furthest along, in Phase 3 clinical trials, while GSK, Sanofi, Pfizer, and several smaller companies have candidates in earlier stages. Some approaches use novel delivery methods, including an oral vaccine from Vaxart and a nasal spray from Blue Willow Biologics.
Governments also maintain stockpiles of older, conventionally manufactured H5N1 vaccines that could be deployed in an emergency, though these would take time to distribute at scale and may not perfectly match a newly mutated strain. The mRNA platforms are designed to be updated more quickly, which is a key advantage if the virus changes.
For the average person who doesn’t work with livestock or poultry, the current risk of bird flu remains very low. The virus has not gained the ability to spread easily between people, and the vast majority of cases trace back to direct animal contact. That calculus would change quickly if the virus acquires the right mutations, which is exactly why public health agencies treat every new human case as an urgent signal worth investigating.