H5N5 is not believed to be a greater threat to human health than the H5N1 virus, which was behind a wave of human infections in the U.S. in 2024 and 2025.
A man in Grays Harbor County, Washington, is believed to be the first person to die from the rare H5N5 strain of bird flu, according to state health officials. Despite the death, authorities emphasized on Friday that the risk to the general public remains low.
The man, an older adult with underlying medical conditions, had been receiving treatment for H5N5 and is thought to be the first known human infected with this particular strain. He lived about 78 miles southwest of Seattle and kept a backyard flock of domestic poultry that had been exposed to wild birds, which is believed to be the likely source of infection.
State health officials said no other individuals connected to the case have tested positive for avian influenza. They are monitoring everyone who had close contact with the man, but there is no evidence of person-to-person transmission of the virus.
Earlier this month, the Centers for Disease Control and Prevention (CDC) stated that nothing about this case suggests an increased risk to public health.
The H5N5 strain is not considered more dangerous to humans than H5N1, the avian flu virus responsible for a surge of about 70 human infections in the U.S. during 2024 and 2025. Most of those cases involved mild symptoms in workers on dairy and poultry farms.
The scientific distinction between H5N5 and H5N1 lies in a specific viral protein that helps release the virus from infected cells and allows it to spread to nearby cells. This difference affects how each strain behaves biologically, but current evidence does not suggest that H5N5 poses a greater threat to humans.