CDC: Drug-resistant 'dual mutant' flu strains detected in US

Two cases of “dual mutant” strains of influenza A, or H1N1, have been detected in the United States.

Researchers warn that these genetic changes might make flu treatments less effective.

Earlier this year, scientists in Hong Kong published findings on two mutations, I223V and S247N. Their research suggested that these mutations could reduce the effectiveness of oseltamivir, the most commonly prescribed treatment for influenza. Most people know it as Tamiflu.

As for how much these mutations might reduce oseltamivir's effectiveness in real-life situations, that we don’t know for certain.

However, lab tests showed that the mutated viruses were up to 16 times less sensitive to the antiviral medicine. On the positive side, this decrease is not as large or as severe as what's been seen with some previous mutations that caused concern.

Now, a new analysis published in the Center for Disease Control and Prevention’s Emerging Infectious Diseases journal reported that these two dual mutants strains were collected in the United States.

Tests indicated that these strains also demonstrated a reduced susceptibility to other approved influenza antiviral drugs including baloxavir. Baloxavir is a newer antiviral medication.

While the researchers said the emergence of antiviral-resistant variants is a concern for public health, the CDC is not overly worried at this point.

Since the mutations first appeared in May 2023, cases have been reported from 15 countries across five continents. A total of 101 virus samples were shared with the global virus database GISAID from countries across Africa, Asia, Europe, North America and Oceania.

The two countries with the highest number of reported cases include the Netherlands, with 30 reported cases, and France, with 24 reported cases. However, these mutations are still considered rare, making up less than 1% of flu virus sequences globally.

As for the upcoming flu season, it's unclear how widely these mutated viruses will spread. But with or without these mutations, the flu vaccination remains important as it still offers protection.

The CDC also emphasizes the importance of early antiviral treatment for hospitalized flu patients and those at risk of severe illness. They will continue to monitor and track any new spread and genetic changes.

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