Laboratory methodologies for testing the antiviral susceptibility of influenza viruses:
Reference viruses for validation and controls

Reference viruses for NAI susceptibility assays

Reference viruses are necessary for the quality control of phenotyping neuraminidase (NA) enzyme inhibition assays and genotyping molecular-based assays in determining the NAI susceptibility of viruses. Although the same reference influenza viruses can be used for both methodologies, there are certain differences that need to be considered.

Phenotyping neuraminidase enzyme inhibition assays

To assist in the establishment of neuraminidase inhibition assays and standardization of IC50 values, the isirv-Antiviral Group (the isirv-AVG, formerly NISN) has assembled a panel of eight reference viruses. This panel includes type A (subtypes H1N1, H1N1pdm09 and H3N2) and type B viruses.

The reference virus panels are available without a material transfer agreement (MTA) and are free of charge, although shipping expenses must be covered by the recipient laboratory. All requests should be submitted through the isirv-AVG web site:

Other reference viruses can be requested from WHO Collaborating Centres in GISRS.

Genotyping molecular-based assays

Reference virus variants for genotyping molecular-based assays are not currently available. To facilitate the validation of genotypic assays used for the detection of the H275Y substitution in A(H1N1)pdm09 viruses, WHO is exploring the possibility of including virus variants in the WHO GISRS External Quality Assessment Project for virus detection by PCR.