by Seattle, WA – Health officials in Washington State have confirmed the first known human infection with the H5N5 bird flu virus, marking a significant development in avian influenza cases. The infected individual, an older adult with underlying health conditions, remains hospitalized as authorities continue their investigation.
A New Strain of Bird Flu Emerges in Humans
On November 14, 2025, the Washington State Department of Health announced that the infected person contracted a strain different from those previously seen in the U.S. The bird flu strain, H5N5, has not been reported in humans before, making this the nation’s first case since February.
The infected individual kept a mixed backyard flock exposed to wild birds, which are considered the likely source of the infection. Public health experts are examining all possible transmission pathways to better understand this new case.
Comparing H5N5 to H5N1: What Experts Say
While the H5N5 virus is new to humans, experts emphasize that its threat level is not believed to surpass that of the H5N1 virus, which caused more than 70 human infections in the U.S. during 2024 and 2025, mostly mild cases among farm workers.
“These viruses behave similarly,” said Richard Webby, a leading flu researcher at St. Jude Children’s Research Hospital. “My gut instinct is to consider it the same as H5N1 from a human health perspective.”
The Centers for Disease Control and Prevention (CDC) echoed this sentiment, stating no current evidence suggests this case increases the risk to public health. They are currently awaiting samples from Washington for further testing.
Dr. Webby further explained, “Think along the lines of different brands of car tires. They both do the same job, it’s just each is better tuned for specific conditions, which we don’t fully understand.” The distinction between H5N5 and H5N1 lies in a protein affecting virus spread within the host.
Bird Flu’s Reach Extends Beyond Birds
Since January 2022, bird flu has been detected in various bird populations. In March last year, the virus was identified in dairy cows for the first time, showing its capability to infect multiple species. This virus affects birds, as well as mammals such as pigs, cattle, and cats. Human infections typically occur through close contact with infected animals, placing farm and poultry workers at the highest risk.
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- First human H5N5 case confirmed in Washington state
- Older adult with underlying health conditions hospitalized
- Backyard flock exposed to wild birds likely infection source
- CDC confirms no increased public health risk at present
- H5N5 and H5N1 viruses behave similarly according to experts
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What Happens Next?
Health officials continue close monitoring of the case while advancing investigations to understand the virus’s transmission dynamics. The public is encouraged to stay informed about bird flu developments and practice prudent precautions, especially when interacting with birds or farm animals.
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