To improve reporting of viruses with reduced susceptibility, a criteria was standardised in 2012 by the WHO working group on influenza antiviral susceptibility (WHO-AVWG) [28], such that influenza A viruses with a 10–100 fold increase in OST IC50 compared to a susceptible human influenza virus of the same NA subtype were described to have ‘reduced inhibition’, while those with greater than a 100-fold increase in OST IC50 were described as having ‘highly reduced inhibition’. This evidence concerns the gene XK and influenza.