US reports its first fatal case of H5N1 bird flu

A man in Louisiana has become the first recorded fatality in the US attributed to the H5N1 strain of avian influenza currently causing a major outbreak in the poultry and dairy farming sectors.

The man – who was aged over 65 and had underlying medical conditions – was hospitalised a week ago after contracting bird flu after exposure to "a combination of a non-commercial backyard flock and wild birds," said the Louisiana Department of Health.

The unidentified man is one of 66 confirmed human cases of H5N1 bird flu in the US since 2024, when the current outbreak took hold, mostly from exposure to animals or consumption of poorly cooked meat, with just one other case recorded from 2022, according to the Centers for Disease Control and Prevention (CDC).

To date, most cases of the infection have been relatively benign, although the situation in other countries is rather different. There have been around 950 cases of H5N1 bird flu in humans reported to the World Health Organization (WHO), around 50% of which have resulted in the patient's death – which is a considerably higher mortality rate than COVID-19, at around 4% and seasonal flu at 1%.

The CDC said it remains encouraged that no person-to-person transmission spread has been identified with H5N1 – although, in September the first case without exposure to sick or infected animals was reported. The agency has also not seen any virologic changes actively spreading in wild birds, poultry, or cows that would raise the risk to human health.

"CDC has carefully studied the available information about the person who died in Louisiana and continues to assess that the risk to the general public remains low," it said in a statement.

Nevertheless, there are still concerns that the scale of the ongoing epidemic in birds – which has claimed the lives of around 280 million animals since October 2021 – as well as the outbreak in cattle in the US, could raise the risk of the virus evolving to become a threat.

Along with the biggest decline in wild bird populations in decades, there have been thousands of recorded deaths among mammals like seals and sea lions that live in close proximity to sea birds. The spread in mammals that have close contact with humans is concerning for public health experts, as it gives the virus more opportunities to make the jump to people.

A recent scientific paper found that a single mutation in H5N1 could be enough to allow the virus to infect humans more readily, while a few months ago a man in Mexico became the first recorded human fatality linked to the H5N2 strain of bird flu.

The developments reinforce the need for close monitoring of H5 flu viruses to try to get ahead of potential mutations that could precipitate an outbreak in humans and for the stockpiling of vaccines against potential pandemic strains like H5N1.

In June, the US federal government ordered 4.8 million doses of a vaccine developed by CSL Seqirus that is matched to the H5 antigen of the currently circulating H5N1 strain, and contracted Moderna to develop an mRNA-based 'pre-pandemic' flu vaccine the following month, but has said it has no plans yet to authorise an immunisation programme.

Photo by Brooke Cagle on Unsplash