Figure 1. Molecular and serological characterization of influenza strains used in the study. Phylogenetic tree based on sequence analysis of the region codifying for the globular head region of haemagglutinin of strains used in the study, amino acid mutations onto-antigenic sites with respect to vaccine A/California/04/09(H1N1)pdm09 strain and serological characterization of isolated and reference viruses, performed with the HI test using whole viruses and post-infection ferret sera.