2.3. NA inhibition assay

Fluorescence-based NA inhibition assays were performed using the fluorogenic substrate MUNANA, live viruses and NA inhibitors: oseltamivir carboxylate (OSE; MedChem Express), zanamivir (ZAN; Sigma-Aldrich) and peramivir (PER; SelleckChem) as described elsewhere (World Health OrganizationWHO Global Influenza Surveillance Network, 2011). Virus drug resistance was classified according to the WHO recommendations based on the fold increase in IC₅₀ compared to the susceptible reference strain (wt NA): normal inhibition (NI) < 10-fold; reduced inhibition (RI) 10 to 100-fold; highly reduced inhibition (HRI) > 100-fold. (Anonymous, 2012).