Contribution of neuraminidase of influenza viruses to the sensitivity to the serum inhibitors and reassortment efficiency

: The live attenuated influenza vaccine (LAIV) consists of reassortant viruses with hemagglutinin (HA) and neuraminidase (NA) gene segments inherited from the circulating wild-type (WT) parental and the 6 internal protein-encoding gene segments from the cold-adapted attenuated master donor viruses (genome composition 6:2). In this study, we describe the obstacles to developing LAIV vaccine strains depending on the phenotypic peculiarities of the WT viruses used for reassortment. The genomic composition analysis of 849 reassortants revealed that over 80% of the reassortants based on the inhibitor-resistant WT viruses inherited WT NA as compared to 26% of reassortants based on the inhibitor-sensitive WT viruses. In addition, the highest percentage of the vaccine genotype reassortants was achieved when WT parental viruses were resistant to the non-specific serum inhibitors. We demonstrate that NA may play a role in the influenza virus sensitivity to the non-specific serum inhibitors. Replacing NA of the inhibitor-sensitive WT virus with the NA of the inhibitor-resistant master donor virus significantly decreased the sensitivity of the resulting reassortant virus to the non-specific inhibitors.