Saira Hussain, Charmaine Chia, Ashwin Muraleetharan, Yi-Mo Deng, Xiaomin Dong, Presa Chanthalavanh, Emi Takashita, Clyde Dapat, Jessica E Miller, Heidi Peck, Raphael T C Lee, Jan Williamson, Louise Cooley, Sebastian Maurer-Stroh, Ian G Barr
The emergence of viruses with reduced susceptibility to antivirals poses an ongoing risk which could limit their effectiveness. Here we report a cluster of A(H3N2) viruses detected in Tasmania, Australia, with a PA gene mutation A37T that showed mild reductions in susceptibility in vitro to baloxavir (3.47- to 16.33-fold increased EC50) when compared to wild-type influenza A(H3N2) viruses. When the PA-A37T and PA-I38T substitutions were combined and tested in IRINA assay, eightfold higher inhibition was seen compared to PA-I38T alone. On-going monitoring of influenza viruses for reduced susceptibility to antivirals remains an important part of seasonal and zoonotic influenza surveillance.