What To Know About Bird Flu After The First US Death

By Gerry Smith, Ilena Peng & Riley Griffin

For influenza viruses, imperfection is a strength. They constantly mutate, producing new strains that challenge immune systems primed to fight earlier varieties. That’s what makes flu a life-long threat to humans and the animal species — mainly birds — that are vulnerable to it.

Since 2020, a strain of highly pathogenic avian influenza called H5N1 has been decimating flocks of domestic and wild birds. The epicenter is now in the US, where it’s spreading among dairy cows and has infected dozens of people, primarily farmworkers exposed to sick animals. In January, a patient in Louisiana who tested positive for bird flu died, marking the first US fatality linked to the respiratory virus.

The US Centers for Disease Control and Prevention and the World Heath Organization say the overall risk to the general public remains low, but public-health officials are on alert for any indication of the most feared outcome: human-to-human transmission that could trigger a pandemic.

When did H5N1 begin spreading?

The H5N1 strain was first discovered in 1996 in geese bred in southern China. It’s proved to be alarmingly adept at jumping continents and species and has rampaged through captive, commercial birds across the globe; governments ordered millions of birds slaughtered to limit the contagion.

A variant that emerged in 2020, clade 2.3.4.4b, led to infections in mammals like farmed mink in Spain and Peruvian sea lions. The same strain is ripping through wild birds and poultry in the US and has gained a foothold among dairy cows, with cases popping up among people who work with sick animals.

While those infections spurred heightened attention, the period from 2017-2024 has been the quietest period of H5N1 activity in humans since the virus first appeared, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

How bad is bird flu for humans?

From 2020-2024, 78 confirmed human cases of H5N1 had been reported globally to the World Health Organization, resulting in nine deaths. The health implications in most US cases have been limited; symptoms have been treatable with antiviral drugs.

What are the symptoms?

There have been dozens of reported cases in the US since the 2024 outbreak began, mostly farmworkers in close contact with dairy cows or poultry, many of whom reported irritated eyes. Health authorities are looking for conjunctivitis, also known as pink eye, as an indication that someone may be infected with bird flu. Eyes are the only part of the human body with “avian” receptors that the virus is adept at attaching to.

Some patients have experienced upper respiratory infections, raising concerns about transmission. The CDC is monitoring the virus for genetic mutations that could make it more dangerous. As of December, there continues to be no evidence of human-to-human spread, the CDC said.

How are people infected with bird flu treated?

Anyone with a suspected or confirmed infection should be treated immediately with one of the antiviral drugs known as neuraminidase inhibitors, such as Roche Holding AG’s Tamiflu, according to the CDC. Patients should get the medicine regardless of the severity of the disease or the length of time since symptoms began, the agency said. It also issued, on an emergency basis, instructions to medical professionals on how to give drugs like Tamiflu preventively to people who have been exposed to the viruses with pandemic potential, in an effort to block infection.

Is there a bird flu vaccine for humans?

Bird flu vaccines are being stockpiled, but aren’t currently available to the public. The US asked vaccine-maker CSL Seqirus to produce 4.8 million doses last summer, to add to hundreds of thousands already on hand. However, experts warn a future strain of the virus that transmits between humans would likely require a different shot. The CDC isn’t recommending immunization for farmworkers because infections have been relatively mild, Nirav Shah, principal deputy director of the CDC, said in July.

The US Department of Health and Human Services awarded Moderna Inc. $176 million for testing an mRNA vaccine that targets several influenza strains, including the current bird flu viruses. The hope is that the newer technology could be quickly updated if needed.

The US Department of Agriculture, meanwhile, is looking into a potential H5N1 vaccine for cows, said Eric Deeble, acting senior adviser for H5N1 response. The agency has approved several field safety trials for vaccines designed to protect cows from the bird flu.

How many US cows and birds have been impacted?

As of early January, 917 cow herds across 16 states have tested positive for bird flu. California, the biggest US milk producer, declared a state of emergency to help expedite a response as the outbreak sweeps through its dairy herds. The CDC has previously said it believes the cows are transmitting it to each other via contact with infected milk. Commercial milking machines are often used on dozens of cows per day, and milk droplets can remain infectious on contaminated equipment for hours.

The number of reported cases is likely an underestimate due to testing challenges, Osterholm said. Wastewater surveillance tools used to detect Covid-19 are now being used to track bird flu in humans and cattle. The testing of dairy cows moving between states has been required since late April, and the USDA further bolstered surveillance by issuing a federal order on Dec. 6 for the national collection and testing of raw milk samples. Dairy farmers will also need to share epidemiological information to aid with contact tracing.

US officials haven’t recommended the destruction of infected cows, which often recover, while millions of birds have been culled. The virus has affected more than 130 million birds across the country.

While milk from infected cows, which may be discolored or thickened, is being diverted or destroyed, the losses shouldn’t have a major impact on supply, according to the USDA.

So long as dairy products have been pasteurized, a process that kills viruses and most bacteria, products such as milk, cheese and ice cream are safe for consumption. US health agencies suggest that Americans avoid raw milk and unpasteurized products.

What are scientists looking for?

Scientists recently discovered that cow udders contain receptors that avian and human influenza viruses can latch onto. Having both kinds of receptors makes it possible for other animals such as pigs to transmit diseases between species, which is what happened with the deadly 2009 swine flu pandemic. The finding raises concern about what might happen if a cow gets simultaneously infected with bird flu and human influenza. In late October, government officials said a pig kept on a backyard farm in Oregon tested positive for the H5N1 bird flu for the first time in the US, a development that scientists have feared because it could help the virus further evolve and put humans at risk.