Optimization of influenza A vaccine virus by reverse genetic using chimeric HA and NA genes with an extended PR8 backbone.

The yield of influenza antigen production may significantly vary between vaccine strains; for example the A/California/07/09 (H1N1)-X179A vaccine virus, prepared during 2009 influenza pandemic, presented a low antigen yield in eggs compared to other seasonal H1N1 reassortants. In this study a bi-chimeric virus expressing HA and NA genes with A/Puerto Rico/8/34 (H1N1) (PR8) and X179A domains was rescued by reverse genetics using a mixture of Vero/CHOK1 cell lines (Medina et al. [7]). The bi-chimeric virus obtained demonstrated to yield much larger amounts of HA than X179A in eggs as measured by single-radial-immunodiffusion (SRID), the reference method to quantify HA protein in influenza vaccine. Such kind of optimized virus using PR8 backbone derived chimeric glycoproteins could be used as improved seed viruses for vaccine production.