Susceptibility of I38-substituted viruses to baloxavir acid (BXA) was determined by plaque reduction assay, and fold change (FC) was calculated as relative EC₅₀ of each tested virus to that of the cognate wild-type virus. Bold, clinically confirmed amino acid substitutions.

^aData from reference.¹⁰

^bData obtained from the current study is shown, while FCs of A(H1N1) viruses with I38S and I38L were previously reported as 52- and 9-fold, respectively.²⁵

^cThe recombinant PA/I38R viruses were not reverse-genetically rescued.