Drug-resistant 'double mutant' flu strain now being tracked in U.S., CDC says

The Centers for Disease Control and Prevention said Wednesday that at least two cases of the so-called “double mutant” strain of H1N1 influenza have been detected in patients in the United States — a genetic mutation that could make vaccines less effective. Main influenza antiviral drugs What hospitals rely on.

New Analysis H1N1 influenza virus These two worrying mutations — which scientists call I223V and S247N, and represent changes in a key surface protein of the virus — Published The findings are published this week in the agency's Emerging Infectious Diseases journal.

This follows reports by scientists in Hong Kong who were the first to test this mutation, finding that in their laboratory experiments: Published in MarchThe team found that the two mutations may make H1N1 more resistant to the flu treatment oseltamivir, commonly sold by the pharmaceutical company Roche under the brand name Tamiflu.

It's unclear how much the mutation actually reduces the effectiveness of oseltamivir: Laboratory tests have found that the mutated virus is up to 16-fold less susceptible to antiviral drugs, though that's a smaller reduction than previous worrying mutations.

“These mutant viruses maintain susceptibility to other influenza antivirals, including the newer baloxavir marboxil. There is no immediate impact to change clinical treatment decisions,” a CDC spokesperson said in an emailed statement. Flu vaccination It still provides protection against viruses with these mutations.

Cases across multiple continents

Despite the “rapid spread of the double mutant across countries on different continents,” the CDC report on the new double mutant influenza strain noted that the mutation still appears to be rare for now.

A total of 101 sequences from Africa, Asia, Europe, North America and Oceania have been submitted to the global virus database GISAID since the mutation was first identified in a sample taken in British Columbia, Canada, in May 2023. These represent less than 1% of influenza virus sequences in that period.

“However, due to differences in surveillance and genetic analysis strategies across countries, these data may not necessarily reflect the actual rates in circulation,” the authors said.

The two U.S. cases were detected this fall and winter by a lab at the Connecticut State Department of Health and a lab at the University of Michigan.

“It is unclear to what extent these mutant viruses will circulate during the upcoming season, and it is important to continue to monitor the spread and evolution of these viruses,” a CDC spokesperson said.

Most commonly prescribed antiviral drugs

The CDC has long Closely tracked Potential mutations in influenza viruses may lead to resistance to oseltamivir.

According to the CDC, oseltamivir is the most commonly prescribed influenza treatment. last year It turns out that this drug accounts for 99.8% of influenza antiviral drugs. Prescribed to children.

CDC (Centers for Disease Control and Prevention) prompt Doctors are urging all flu patients who are hospitalized or at risk of severe illness to receive the flu antiviral drug as soon as possible. They are also relying on oseltamivir to treat people with ongoing flu infections. H5N1 avian influenza outbreak At the dairy this year.

This is not the first time health officials have tracked the emergence of a potential threat to the effectiveness of flu treatments.

before being wiped off the map by a competing H1N1 strain. Swine flu pandemic After the influenza A epidemic that swept the world in 2009, health authorities from Europe to Japan reported a surge in H1N1 strains resistant to oseltamivir in 2007 and 2008.

The strain has a mutation called H275Y that made it up to 1,000 times less susceptible to oseltamivir in laboratory tests at the time.