Peculiarities of obtaining attenuated thermosensitive recombinants of influenza A virus at the end of the H3N2 epidemic cycle.

The conditions of obtaining thermosensitive recombinants of the virulent A/Leningrad/82/76 (H3N2) virus with two donors of attenuation, A/Leningrad/134/17/57 (H2N2) and A/Leningrad/9/37/46 (H0N1), were evaluated. The recombinants were obtained by various methodical approaches (hybridization of native viruses, cross-reaction and selection of recombinants at temperatures of 25, 32 and 40 degrees C) to study their effects on the degree of attenuation and the regularity of transmission of the ts marker. The recombinants examined varied in thermosensitivity which depended on the conditions of recombination of parent viruses. All recombinants studied, irrespective of their RCT40 marker, were innocuous for men.