Uncommon drug-resistant flu version recognized in the U.S., according to the CDC.
Flu viruses are always evolving, but a new strain with two worrying mutations may potentially disrupt treatment using oseltamivir phosphate, known commercially as Tamiflu.
"Worldwide surveillance is actively taking place to identify these mutations," states Dr. Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health. "We need to know when they crop up as it could significantly impact how we deal with flu."
At present, experts believe the threat level remains low.
Fifteen nations across five continents have reported cases of the dual-mutated flu variant, which includes two instances in the US, per a report published on Wednesday in the CDC's Emerging Infectious Diseases journal. However, these cases are uncommon, accounting for roughly 1% of the samples gathered between May 2023 and February 2024.
"These mutations seem to show up in multiple places, but they're never the primary virus in any location they appear," Pekosz explained.
"It's not as if the mutation occurred in one place, then the specific virus started spreading and dominating everywhere suddenly in one sweeping wave," he continued. Instead, the same mutations appear to evolve independently in different locations.
The double-mutated strain has demonstrated a reduction in Tamiflu effectiveness of up to 16 times, according to the CDC report; however, this is based on lab studies.
Other flu variants have shown much higher resistance in lab tests, and there's no way to predict what this might mean in real-life clinical settings, suggested Dr. William Schaffner, an infectious disease expert at Vanderbilt University.
"We're not entirely sure what the clinical significance of this slight resistance is," he stated. "It could be that the dosage of Tamiflu provided to patients is sufficient to overcome this."
Lab tests indicate that other antiviral treatments, including a recent antiviral called baloxavir marboxil, or Xofluza, remain effective against the dual mutants, according to the CDC. Additionally, flu vaccines should provide protection against infections caused by viruses with the mutations.
"There are no immediate implications regarding clinical care decisions," the CDC stated in an email. "CDC is consistently monitoring the antiviral susceptibility of circulating seasonal flu viruses in the US and internationally, working alongside global partners. This global virological surveillance will inform the potential public health threat of these flu viruses."
CNN’s Maya Davis contributed to this report.
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The report published in the CDC's Emerging Infectious Diseases journal confirms fifteen nations, including two instances in the US, have reported cases of the dual-mutated flu variant. This uncommon strain accounts for about 1% of the samples collected between May 2023 and February 2024.
According to the CDC report, the double-mutated strain has demonstrated a reduction in Tamiflu effectiveness of up to 16 times in lab studies.
