Certain embodiments of the present invention include a method for rapidly designing pharmaceutical preparations for preventing viral infection that have adapted to growth in various culturing systems but maintain antigenic similarity to the original virus. The method may include serial passaging a plurality of instances of a targeted virus strain from an infected first animal in respective droplets in second animal cells, in parallel synthesizing antibodies that neutralize the targeted virus strain in a third animal, and selecting the second animal cell-adapted viral lineages that are neutralized by the antibodies to identify second animal cell-adapted viral lineages having antigenic similarity to the targeted virus strain.

A method to prepare recombinant influenza viruses comprising a mutant M2 protein which has a deletion of two or more residues in the cytoplasmic tail and is attenuated in vivo, is provided, as well the resulting virus and vaccines with the virus.

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.

Certain embodiments of the present invention include a method for rapidly designing pharmaceutical preparations for preventing viral infection that have adapted to growth in various culturing systems but maintain antigenic similarity to the original virus. The method may include serial passaging a plurality of instances of a targeted virus strain from an infected first animal in respective droplets in second animal cells, in parallel synthesizing antibodies that neutralize the targeted virus strain in a third animal, and selecting the second animal cell-adapted viral lineages that are neutralized by the antibodies to identify second animal cell-adapted viral lineages having antigenic similarity to the targeted virus strain.

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.