What is H5N1? Experts warn virus spreading across US, fears of new pandemic
Experts warn about the possibility of a new pandemic in 2025 as bird flu spreads across all 50 states, impacting American dairy and poultry farms with dozens of people infected.
Here's what to know.
Bird flu, also known as H5N1, has been around for decades. But the discovery in 2024 that the virus spread from wild birds to cows came as a surprise to public health experts, according to officials. In just over a year, the virus has ravaged America's dairy herds and poultry flocks and has infected humans − sometimes causing death.
The Global Virus Network (GVN), a nonprofit coalition of virologists, has issued warnings to governments to address the threat of the H5N1 outbreak by improving surveillance, implementing biosecurity measures, and preparing for potential human-to-human transmission.
"Understanding the current landscape of H5N1 infections is critical for effective prevention and response," said Dr. Sten H. Vermund, chief medical officer of the GVN and an infectious disease epidemiologist. "The virus' ability to infect both animals and humans, combined with recent genetic changes, underscores the importance of proactive surveillance and rapid response measures.”
How much has bird flu spread?
In the United States, the outbreak has affected over 1,000 dairy herds across 17 states, according to U.S. Department of Agriculture data. It has caused the loss or culling in commercial and backyard poultry flocks of more than 169 million birds since 2022, USDA said.
Federal health officials have identified 70 people in the United States infected, mostly among dairy and poultry workers, according to the Centers for Disease Control and Prevention. One person, an older Louisiana resident with underlying medical issues, died in January, becoming the first American death from bird flu. The strain of bird flu the Louisiana resident had, known as D1.1, has been known to cause severe illness in humans.
Bird flu has shown to be concerning elsewhere in North America. In early April 2024, Mexican officials confirmed the country's first bird flu death in a 3-year-old girl. In November 2024, Canadian officials identified a 13-year-old girl who became severely ill with the D1.1 strain and had to be intubated.
“In the U.S. sporadic human infections with no known contact with infected animals highlight the possibility of viral adaptation for efficient human-to-human transmission,” GVN scientists said in a report. “Concurrently, the virus continues to circulate in wild birds, backyard flocks, and hunted migratory species, further amplifying the risk to humans and domestic animals.”
Dr. Kay Russo, a veterinarian, warned in an interview that time to stop the bird flu is “running out.” She told CBS News that while it's not clear how the virus was spreading from cow to cow, “milking equipment is a prime suspect” and workers in milking parlors have also fallen sick with flu-like symptoms.
Infectious disease physician Dr. Kamran Khan said in the same interview, that his company, BlueDot, was among the first to flag the virus in China that became the COVID pandemic. He said “the bird flu is just as concerning” and explained how fast the virus has spread among dairy cattle.
What is H5N1?
H5N1, also known as highly pathogenic avian influenza, is a specific strain of influenza A virus. Bird flu is a highly contagious respiratory disease that primarily affects birds, but can also infect other animals, including mammals like dairy cows and humans.
Chickens are highly susceptible to illness and death, while cows appear to recover. Humans have often had mild symptoms, though a few cases have caused serious illness.
Experts have warned that if the virus continues to spread across species, it increases the likelihood of becoming more transmissible to humans and causing more severe illness.
What are the symptoms of H5N1 infection in humans?
The symptoms of H5N1 infection may include fever (often high fever, over 100.4 degrees) and malaise, cough, sore throat and muscle aches. Other early symptoms may include conjunctivitis and other non-respiratory symptoms.
The infection may progress quickly to severe respiratory illness, pneumonia and neurologic changes (altered mental status or seizures), according to the World Health Organization.
Eduardo Cuevas of Paste BN contributed to this report.