The embryonated egg-based platform currently produces the majority of seasonal influenza\nvaccines by employing a well-developed master donor virus (MDV, A/PR/8/34 (PR8)) to generate\nhigh-growth reassortants (HGRs) for A/H1N1 and A/H3N2 subtypes. Although the egg-based\nplatform can supply enough seasonal influenza vaccines, it cannot meet surging demands during\ninfluenza pandemics. Therefore, multi-purpose platforms are desirable for pandemic preparedness.\nThe Vero cell-based production platform is widely used for human vaccines and could be a potential\nmulti-purpose platform for pandemic influenza vaccines. However, many wild-type and egg-derived\ninfluenza viruses cannot grow efficiently in Vero cells. Therefore, it is critical to develop Vero\ncell-derived high-growth MDVs for pandemic preparedness. In this study, we evaluated two in-house\nMDVs (Vero-15 and VB5) and two external MDVs (PR8 and PR8-HY) to generate Vero cell-derived\nHGRs for five avian influenza viruses (AIVs) with pandemic potentials (H5N1 clade 2.3.4, H5N1 clade\n2.3.2.1, American-lineage H5N2, H7N9 first wave and H7N9 fifth wave). Overall, no single MDV\ncould generate HGRs for all five AIVs, but this goal could be achieved by employing two in-house\nMDVs (vB5 and Vero-15). In immunization studies, mice received two doses of Vero cell-derived\ninactivated H5N1 and H7N9 whole virus antigens adjuvanted with alum and developed robust\nantibody responses.
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