The present invention relates to an isolated attenuated influenza virus strain and a live vaccine comprising the same. The isolated attenuated influenza virus strain is prepared by cold-adaptation of a mother strain which carries 6 internal genomes of A/PR/8/34(H1N1) and two surface antigens HA and NA of A/Aichi/2/68(H3N2). The attenuated influenza virus strain and the live vaccine of the present invention are useful for prevention of seasonal influenza episodes and sudden outbreak of influenza pandemics of predicted or unknown identity, since they have safety, efficacy, high production yield, immediate protection against variety of influenza subtypes and prolonged protection against specific influenza subtype.