Virus in Louisiana bird flu patient shows mutations that may increase transmissibility to humans, CDC analysis finds

CNN
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A genetic analysis of samples from the patient in Louisiana recently hospitalized with the nation’s first severe case of H5N1 bird flu shows that the virus likely mutated in the patient to become potentially more transmissible to humans, but there is no evidence that the virus has been transmitted to someone else.

The patient was likely infected after having contact with sick and dead birds in a backyard flock, US Centers for Disease Control and Prevention said earlier this month. In an analysis On Thursday, the agency said the mutations it identified in samples taken during the patient’s hospitalization were not found in the birds, suggesting they are not in the virus that circulates widely in wildlife.

The mutations, similar to those observed in a hospitalized patient in British Columbia, Canada, may make it easier for the virus to bind to cell receptors in the human upper respiratory tract, the agency said in its analysis.

“The changes observed were likely generated by replication of this virus in the patient with advanced disease rather than primarily transmitted at the time of infection,” the CDC said. “While worrisome and a reminder that A(H5N1) viruses can develop changes during the clinical course of a human infection, these changes would be more concerning if found in animal hosts or in early stages of infection… when these changes may be more likely to facilitate spread to close contacts.”

The agency emphasized that the risk to the public has not changed and remains low, but said the detection of the genetic mutations “underscores the importance of ongoing genomic surveillance of humans and animals, containment of avian influenza A(H5) outbreaks in dairy cattle and poultry and preventive measures among people with exposure to infected animals or environments.”

The analysis found no changes associated with markers that could mean antiviral drugs would not work as well against the virus, the CDC added, noting that the samples are closely related to strains that could be used to make vaccines if needed.

The sequences also did not show changes in genes associated with adaptation to mammals, the CDC found. The patient was infected with a strain known as D1.1 that is closely related to viruses circulating in wild birds and poultry in the United States; another strain known as B3.13 has spread widely in dairy cows and has not been shown to cause serious disease in humans in the United States

“While this sounds like good news, the H5N1 situation remains grim,” doctor Angela Rasmussena virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada, submitted on Bluesky Thursday.

“There has been an explosion of human cases,” she said. “We don’t know what combination of mutations would lead to a pandemic H5N1 virus … but the more people are infected, the more likely a pandemic virus will emerge.”

The CDC has confirmed 65 cases of H5N1 bird flu in humans in 2024. Of those, 39 were linked to dairy herds and 23 to poultry farms and slaughter operations. For two cases, the source of exposure is unknown. The serious case in Louisiana is the only one associated with backyard herds.

Dr. Paul Offitta vaccine researcher at the Children’s Hospital of Philadelphia, noted that the CDC said the mutations “may” enable the virus to bind better to cell receptors in the human upper respiratory tract, not that they clearly do.

“I would like to see clear evidence … that it binds well,” Offit told CNN on Friday. “It hasn’t happened yet.”

“And more importantly,” Offit added, “there is not the clinical relevance that you see spread from person to person.”