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The Centers for Disease Control and Prevention (CDC) has identified two human cases of influenza that are resistant to Tamiflu, the most commonly used antiviral flu drug. Laboratory tests confirmed that these two U.S. samples of the influenza virus contained two major mutations, I223V and S247N, which are associated with the most prevalent strain of seasonal flu, influenza A (H1N1).
The CDC’s annual analysis of flu samples from the U.S. and around the world revealed a total of 101 samples of the “dual mutant” version of H1N1, originating from 15 countries across five continents. The earliest detected sample was collected in Canada in May 2023, while the latest were found in Europe in January and February 2024. The Netherlands reported the highest number of these dual mutant flu cases, with 30 samples identified.
Unlike the Tamiflu-resistant strain, these mutated viruses remain susceptible to other, less frequently used antiviral drugs. The dual mutant form was initially reported by scientists studying flu samples from Hong Kong collected in October 2023 and published in The Lancet Microbe.
Flu antiviral medications, including Tamiflu, are known to reduce the severity and duration of flu symptoms when administered promptly—ideally within one to two days of symptom onset. They have also been linked to a lower risk of death among adults hospitalized with the flu.
Since October 2023, the U.S. has experienced approximately 35 million flu cases, resulting in 390,000 hospitalizations and 24,000 deaths, as reported in the CDC’s weekly FluView publication. Public health laboratory testing of flu specimens this season indicates that 76% were Influenza A, with the remaining 24% being Influenza B.
In comparison, a recent analysis published in the Journal of the American Medical Association indicates that COVID-19 continues to be slightly more lethal than the flu among hospitalized adults. The 30-day death rate for adults hospitalized with COVID-19 in the 2023-2024 period was 5.7%, compared to 4.7% for those hospitalized with the flu. Moreover, the number of hospitalizations for COVID-19 was double that of the flu.
These findings highlight the ongoing challenges in managing seasonal flu and underscore the importance of continued surveillance and development of effective antiviral treatments.
