(EN) Provided is a method for constructing a reassortant influenza virus that has genomic segments of at least two types of influenza virus when an antigen strain and a donor strain have analogous antigenicity. The method relies upon a step for using (1) a first influenza virus containing an antigen protein (x), (2) a second influenza virus containing an antigen protein (x’) having antigenicity analogous to that of strain (1), and (3) a third influenza virus containing an antigen protein (y) having antigenicity different from that of strain (1) to infect hosts with strain (2) and strain (3) and co-culture to construct reassortant influenza viruses, and selecting an influenza virus (Y) comprising the antigen protein (y) from among said viruses, followed by infecting hosts with strain (1) and the selected strain (Y), co-culturing, and selecting an influenza virus (X) comprising the antigen protein (x) from the reassortant influenza viruses constructed from strain (1) and strain (Y).
