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 strains A/Leningrad/9/37/46 (H0N1) 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 to be non-reactogenic irrespective of the number of genes inherited from the cold-adapted parent.
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Ghendon et al. (1981) studied this question.
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