Fig. 1

Flowchart for the generation of H7N9 candidate vaccine viruses in serum-free medium by reverse genetics. a The development of egg-derived CVVs by reverse genetics using the high-growth PR8 backbone. Egg-derived CVVs are suitable for egg-based manufacturing systems, but their viral yield in cell-based manufacturing systems (aMDCK cells) is usually low. b The development of cell-derived CVVs by reverse genetics using a high-growth backbone from aMDCK-adapted NIBRG-14. The cell-derived CVVs grown well in egg- and sMDCK-based manufacturing systems in this study