SUMMARY

Temperature-sensitive (ts)mutations occurring in three genes 1, 2 and 7, and 1, 5 and 7 were found in two cold-adapted (ts) attenuated influenza virus trains A/Leningrad/9/37/46 (HON 1) and A/Leningrad/134/17/57 (H2N2) respectively. The recombinants, obtained by crossing these cold-adapted strains with virulent influenza virus strains, had different genome structures and inherited from one to six genes from the cold-adapted parents. Tests of reactogenicity of recombinants in volunteers showed all the recombinants o be non-reactogenic irrespective of th number of genes inherited from the cold-adapted parent