Attenuated ts-recombinants of influenza A/USSR/77 (H1N1) virus obtained by crossing with the cold-adapted donor A/Leningrad/134/57 (H2N2) virus.

Conditions of obtaining attenuated influenza virus recombinants by crossing of a cold-adapted donor with A (H1N1) influenza virus that reappeared in 1977 were studied. Temperature-sensitive recombinants suitable for intranasal immunization of adults with low titres of anti-haemagglutinin and anti-neuraminidase antibodies, and possessing sufficiently high immunogenicity were obtained by crossing of native parent strains and cross-reactivation techniques. It was confirmed that the cold-adapted A/Leningrad/134/17/57 (H2N2) influenza virus variant is a prospective donor of attenuation for obtaining recombinants--candidates for live influenza vaccine strains.