Drug-resistant flu variant identified by the CDC

While bird flu continues to dominate headlines, the more prevalent type of influenza has recently flown under the radar. However, a new study from the Centers for Disease Control and Prevention (CDC) has identified two instances of a drug-resistant flu variant in the US. 

This new strain, labelled a “dual-mutant” variant, merges two flu virus strains—I233V and S247N—into one. Both cases exhibited resistance to standard antiviral treatments.

This dual-mutant strain was initially detected earlier this year in Hong Kong. The CDC, which continuously tracks influenza variations, analysed over 2,000 viral strains from both the U.S. and globally between May 2023 and February 2024. 

More than 100 samples were identified as this dual-mutant strain, with cases reported from over a dozen countries. The most recent detection in Europe occurred in February of this year.

Although this dual-mutant strain is less widespread compared to other flu strains, it’s important to note that flu monitoring practices vary by country. This means the prevalence of the dual-mutant strain could be underreported. Testing revealed that this variant is 16 times less susceptible to Tamiflu, a common antiviral used to alleviate flu symptoms.

In its report. the CDC added that receiving the annual flu vaccine remains the best defence against the flu virus. The vaccine can lessen symptom severity and reduce the risk of hospitalisation and death. The CDC will continue to monitor the development of the variant.

The report adds: “Analysis of available sequence data revealed that dual mutants have been in global circulation since May 2023; overall detection frequency was low. However, those data may not necessarily represent the actual proportion of what was in circulation because of differences in surveillance and sequencing strategies in each country. 

Our study highlights the need to closely monitor evaluation of dual mutants because additional changes may further affect susceptibility to antiviral drugs or provide a competitive advantage over circulating wild-type viruses.”