Antigenic analysis
The viruses were investigated for their antigenic properties by
hemagglutination inhibition (HI) assay with ferret antisera against the
vaccine strains of the influenza season 2019-2020 and A(H1N1)pdm09
vaccine viruses of the influenza season 2020-2021. HI assays employed
turkey and guinea pig red blood cells (the latter for H3N2); viruses
were adjusted to 8 hemagglutinating units for analysis. In order to
generate ferret antisera, intranasal infection of ferrets was performed
with 105 TCID50 of each of the vaccine
viruses and blood was sampled 14 days after infection.