Baloxavir susceptibility of seasonal influenza viruses during the first seven seasons of clinical use in Japan, 2017/18 to 2023/24

Our findings suggest a possible association between the extent of baloxavir use and the emergence of resistance and highlight how circulating subtypes shape seasonal susceptibility profiles. Although reduced susceptibility to baloxavir remains relatively rare, emergence of transmissible virus variants emphasises the need for continued phenotypic and genotypic surveillance to guide treatment strategies, support public health preparedness, and prevent the spread of resistant viruses.