Influenza A(H1N1)pdm09 Virus with Reduced Susceptibility to Baloxavir, Japan, 2024

Area of Science:

• Virology
• Antimicrobial Resistance

Background:

• Influenza A(H1N1)pdm09 is a significant human pathogen.
• Antiviral drug resistance in influenza viruses poses a public health threat.

Purpose of the Study:

• To report the detection of a novel Influenza A(H1N1)pdm09 variant.
• To characterize the in vitro susceptibility and growth of this variant to antiviral drugs.

Main Methods:

• Viral isolation and genetic sequencing.
• Antiviral susceptibility testing (phenotypic or genotypic).
• Viral growth assays.

Main Results:

• Detection of Influenza A(H1N1)pdm09 with I38N substitution in an untreated patient.
• The I38N mutant demonstrated reduced susceptibility to baloxavir.
• The mutant retained susceptibility to neuraminidase inhibitors.
• Reduced viral growth capability was observed for the I38N mutant.

Conclusions:

• The emergence of baloxavir-resistant Influenza A(H1N1)pdm09 warrants ongoing surveillance.
• Antiviral susceptibility monitoring is essential for informing treatment guidelines and public health interventions.
• Understanding resistance mechanisms aids in predicting viral evolution and managing influenza outbreaks.