Dual Mutant H1N1 Strain Detected in U.S.: Potential Threat to Flu Treatment Efficacy

Two human cases of the new "dual mutant" strains of H1N1 influenza have been reported in the United States, according to the Centers for Disease Control and Prevention (CDC). These strains exhibit genetic changes that could potentially reduce the effectiveness of the primary flu antiviral medication used in hospitals.

Identification of Concerning Mutations

Recent analysis published in the CDC's Emerging Infectious Diseases journal highlighted two significant mutations, I223V and S247N, affecting key surface proteins of the H1N1 flu virus. These mutations were initially identified by scientists in Hong Kong, who observed increased resistance to the antiviral drug oseltamivir, commonly known as Tamiflu, in lab experiments conducted earlier this year.

Global Spread and Rarity

Despite the rapid spread of these dual mutant strains to various countries across continents, the CDC's report indicates that they remain relatively rare at present. Since the initial detection of the mutations in a case from the Canadian province of British Columbia in May 2023, a total of 101 sequences have been submitted to the global virus database GISAID from regions including Africa, Asia, Europe, North America, and Oceania. However, these sequences constitute less than 1% of the total flu virus sequences during that period.

U.S. Cases and Surveillance Challenges

The two U.S. cases were identified by laboratories at the Connecticut Department of Health and the University of Michigan during the fall and winter. The authors of the report cautioned that differences in surveillance and sequencing strategies among countries may affect the accuracy of the data, emphasizing the need for comprehensive monitoring and analysis.

Oseltamivir as the Primary Antiviral Treatment

Oseltamivir has been the most commonly prescribed antiviral for flu treatment, comprising 99.8% of antivirals administered to children, as revealed in a study published last year. The CDC has consistently emphasized the importance of early administration of flu antivirals to hospitalized patients and individuals at risk of severe disease.

Historical Precedents and Ongoing Concerns

This development is not the first instance where health authorities have observed potential threats to the effectiveness of flu treatments. Prior to the H1N1 strain responsible for the 2009 swine flu pandemic, health authorities worldwide reported the emergence of an oseltamivir-resistant H1N1 strain in 2007 and 2008.

These findings underscore the ongoing efforts of public health agencies, including the CDC, in monitoring and addressing infectious disease outbreaks and potential treatment challenges.