News release

From: Springer Nature

The highly pathogenic H5N1 virus — commonly known as bird flu — has been detected in 68 humans across the United States as of February 2025, with most of the individuals having been in contact with infected animals. H5N1 has also been detected in dairy cows, which increases the risk of human infection through contaminated raw milk, such as through droplet inhalation, droplets splashing into the eyes or consumption. Current treatment options for H5N1 are limited to existing influenza drugs, such as oseltamivir. However, the effectiveness of these treatments in humans is unclear owing to the severity of the disease, which has prevented human studies.

Richard Webby and colleagues compared the effectiveness of oseltamivir and baloxavir treatment in mouse models of H5N1 infection. Mice were infected with contaminated cow’s milk to mimic typical exposure routes through the mouth, nose and eyes. Mice were treated with either oseltamivir twice a day for 5 days or a single dose of baloxavir. Baloxavir treatment was found to improve disease outcomes, with survival rates of mice infected through the mouth, nose and eyes reaching up to 25%, 75% and 100%, respectively, whereas mice treated with oseltamivir experienced lower survival rates, with mouth, nose and eye infection reaching up to 25%, 40% and 63%, respectively. Webby and colleagues found that orally infected mice were more difficult to treat with either drug and suggest that this is likely due to the virus’s ability to spread faster through the gastrointestinal tract.

Although further testing is required, the authors suggest that baloxavir could be considered, in addition to oseltamivir, for the potential treatment of severe H5N1 infections in humans.