Guidance for clinical and public health laboratories testing for influenza virus antiviral drug susceptibility in Europe

Phenotypic neuraminidase enzyme inhibition assays are recommended to determine the level of inhibition of the neuraminidase enzyme by antiviral drugs as a measure of drug susceptibility of the virus. Genotypic assays are recommended to identify amino acid substitutions in the neuraminidase and M2 ion-channel proteins that have been associated with reduced antiviral susceptibility previously. By 2012 all circulating seasonal influenza A(H1N1)pdm09 and A(H3N2) viruses were naturally resistant to the M2 ion-channel blockers, so priority should be given to testing for neuraminidase inhibitor susceptibility.