First Human H5N1 Death in the US — Just the Beginning?

The recent detection of a new strain of H5N1 bird flu in US dairy herds has raised alarms among scientists. A US Department of Agriculture report noted that the D1.1 genotype has a mutation that may facilitate the virus spread in mammals, including humans. Concerns are growing amid disruptions in epidemiological data sharing under the Trump administration.

First US Human Case

Nevada reported its first human case of bird flu in an agricultural worker exposed to infected dairy cattle. Health authorities in Central Nevada announced the case on February 10, stating that the worker was recovering after experiencing conjunctivitis, the most common symptom reported in infected humans in the United States. Close contacts and other exposed workers were notified and monitored for symptoms. They were offered personal protective equipment, testing, and antiviral medication.

This new case brought the total number of infections in the US bird flu outbreak since April 2024 to nearly 70, mostly among dairy workers. In early 2025, the Louisiana Department of Health reported the death of the first patient in the United States with a confirmed case of avian influenza, an individual over 65 years of age who died after being hospitalized.

Mutation Sparks Alarm

Concerns about the spread of the H5N1 outbreak intensified after the US Department of Agriculture confirmed the presence of a second strain of bird flu in dairy cows in Nevada, marking the first such detection.

The newly identified strain, D1.1, was the dominant genotype in wild birds during the past fall and winter and has also been detected in poultry, according to federal health agencies.

Although US authorities stress that there is no evidence of human-to-human transmission at this stage and that the Centers for Disease Control and Prevention (CDC) considers that bird flu presents “only a low risk to the public,” the variant found in Nevada remains a cause for concern.

The D1.1 genotype was the dominant strain in migratory wild birds during the winter of 2024-2025. However, the Nevada cases marked the first detection of a genotype other than B3.13 in dairy cows in the United States. This represents only the second known instance of a virus spreading from wild birds to dairy cows.

According to Nevada officials, affected dairy workers reported unusually high wild bird deaths near their farms.

The situation is further complicated by genetic sequencing of the D1.1 viruses, which has identified a mutation known to enhance RNA polymerase activity and increase replication efficiency in mammalian cells. This could potentially affect viral pathogenesis in infected mammals, according to a technical note from the US Department of Health.

“This can be of significant concern if this virus continues to spread among cows and infects more people,” said Rick Bright, PhD, an American immunologist and former chief executive officer of the Pandemic Prevention Institute at The Rockefeller Foundation, in an interview with Fortune magazine.

“This mutation has not been associated with improved human transmission, so there are no telling signs of enhanced spread yet. But when this virus gets into people, it is ready to cause a much more serious disease than the (B3.13) virus that has been circulating in cows before now,” he added.

The D1.1 genotype has been linked to several severe human cases of highly pathogenic avian influenza, including a near-fatal infection in a teenage girl in Canada and the first and only human death from avian influenza in the United States, involving a person aged over 65 years in Louisiana.

“We’re closer than ever to a pandemic with this virus,” Bright warned. “And we’re not yet doing everything we can to prevent it or reduce the impact if it does happen.”

Jürgen Richt, DVM, PhD, a leading veterinary scientist and director of the Center for Emerging and Zoonotic Infectious Diseases at Kansas State University, Manhattan, Kansas, emphasized the growing concerns about D1.1’s potential virulence.

“Given the fact that D1.1 seems to be more virulent in humans, this could indicate a major change in terms of public health risks from the earlier scenario with the B3.13 strain,” he told Fortune magazine.

Restricted Public Health Information

Concerns over avian flu preparedness are further compounded by recent political shifts in the United States. Since January 21, the US Department of Health and Human Services has frozen most external communications, including health documents and guidance, until new officials are appointed to review and approve them.

As a result, for the first time in over 60 years, the CDC’s Morbidity and Mortality Weekly Report— a public health publication — was not published on January 23 and 30. Publication resumed on February 6, but according to The Washington Post, there was no mention of the avian flu outbreak or information about the three studies on H5N1 that were scheduled to be published in January.

France’s Proactive Response

Despite concerning global trends, including species jumps in the United States, France has remained unaffected, according to Eric Cardinale, scientific director of Animal Health and Welfare at the French Agency for Food, Environmental and Occupational Health & Safety.

Strict surveillance and biosecurity measures are in place, alongside a nationwide duck vaccination program that has immunized 62 million ducks since October 2023 to reduce viral circulation and prevent strain reassortment.

So far, France has reported only 15 outbreaks this season compared with widespread cases in the United Kingdom, suggesting the strategy is working. On the human health front, authorities are monitoring at-risk populations through the SAGA protocol while working on candidate vaccines and stockpiling efforts.

“We remain extremely vigilant and cautious, but overall, the situation is reassuring,” Cardinale concluded.

This story was translated and adapted from Medscape’s French edition using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.