A number of improvements for preparing vaccine antigens from disintegrated influenza viruses are disclosed. A splitting step can be followed by detergent exchange. Splitting can take place in the presence of a buffer with a higher ionic strength and/or in the presence of phosphate buffer.

Modified influenza virus neuraminidases are described herein that improve viral replication, thus improving the yield of vaccine viruses. Expression of such modified neuraminidases by influenza virus may also stabilize co-expressed hemagglutinins so that the hemagglutinins do not undergo mutation.

A number of improvements for preparing vaccine antigens from disintegrated influenza viruses are disclosed. A splitting step can be followed by detergent exchange. Splitting can take place in the presence of a buffer with a higher ionic strength and/or in the presence of phosphate buffer.