Figure 4.

Virologic analyses on influenza viruses circulating in the community through the national influenza laboratory surveillance network. Influenza isolates collected from regional commissioned laboratories are sent to the national influenza center at TCDC for characterization of viral genetic and antigenic properties. Combined data from genomic sequencing and hemagglutination inhibition assays are used to identify the predominant and new variant virus strains; the antiviral susceptibility pattern of a virus is also inferred from sequences of a particular viral gene segment. Post-infection ferret sera are prepared routinely against both predominant and variant strains, which are used as reagents in antigenic analysis by hemagglutination inhibition assay.