Patent ID: 7384774

Claim:
A method for producing influenza virus particles for preparation of a vaccine, comprising: growing reassortant influenza viruses to produce virus particles and recovering said produced virus particles, wherein said reassortant influenza viruses are produced in cultured cells in the absence of helper virus by introducing into said cultured cells expression vectors sufficient to produce in said cells the genomic vRNA or antigenomic vRNA (cRNA) segments of said reassortant influenza viruses and producing in said cells a nucleoprotein and an RNA dependent RNA polymerase so that RNP complexes containing the genomic vRNA segments of said reassortant influenza viruses are formed wherein said expression vectors encode HA, NA, non-HA and non-NA vRNA segments and wherein the HA and NA vRNA segments are HA and NA vRNA segments of a viral strain different from a strain that contains all of the non-HA and non-NA vRNA segments.