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“Two mutant” strains of the flu have been identified in 15 countries, including two cases in the United States, the CDC said.
CNN
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A rare strain of the flu that has shown some resistance to commonly used antiviral drugs has been found in at least two people in the United States, according to the US Centers for Disease Control and Prevention.
Influenza viruses mutate constantly, but this mutation has two mutations at sites that make treatment with oseltamivir phosphate, also known as Tamiflu, less effective.
“There is active worldwide surveillance to look for these mutations,” said Dr. Andy Pecos, a virologist at the Johns Hopkins Bloomberg School of Public Health. “We want to know when they’re coming because that could really have big implications for how we deal with influenza.”
But now the risk is low, experts say.
Cases of the “double mutant” influenza variant have been identified in 15 countries on five continents, including two cases in the United States. Report It was published Wednesday in the CDC’s journal Emerging Infectious Diseases. But they are rare, representing only about 1% of samples collected between May 2023 and February 2024.
“They show up in a lot of places, but they’re not the dominant virus everywhere they show up,” Pekosz said.
“It’s not like a mutation happened somewhere, and all of a sudden that particular virus started to spread in a big wave and outcompete everything,” he said. Instead, the same mutation appears to be evolving independently at different sites.
According to a CDC report, doubling the effectiveness of Tamiflu has been reduced by up to 16 times – but that’s based on laboratory studies.
Other strains of influenza have shown greater resistance in the laboratory, and there is no measure of what this might mean in real-life clinical practice, said Dr. William Schaffner, an infectious disease expert at Vanderbilt University.
“We don’t really know what the clinical significance of this small resistance is,” he said. The dose of Tamiflu we give to a patient may be sufficient to overcome this.
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Laboratory testing has shown that other antiviral treatments — including baloxavir marboxil or a new antiviral called Xofluza — are still effective against the double mutation, the CDC reports.
And flu vaccines should protect against mutations caused by viruses as well.
“There are no immediate implications for clinical care decisions,” the CDC said in an emailed statement. “CDC, along with international partners, continuously monitors the antiviral susceptibility of seasonally circulating influenza viruses in the US and internationally. This global virological surveillance informs the public health threat of these influenza viruses.”
CNN’s Maya Davis contributed to this report.