IMMUNOGENICITY FOR MICE OF ATTENUATED REA SSORTANTS OF A LENINGRAD/134/47/57 (II2N2) INFLUENZA-VIRUS WITH DIFFERENT GENOME COMPOSITION/

Reassortants of cold-adapted strain A/Leningrad/134/47/57 (H2N2) and v irulent strain A/PR/8/34 (H1N1), modeling genomic composition of vacci nal strains, were tried in mouse experiments. Reassortants' genomes in cluded the major part (5, 6, or 7) from cold-adapted strain and 1 to 3 genes of virulent strain. All the tested reassortants did not differ by temperature sensitivity or cold adaptation phenotypes, did not caus e the death of mice, but differed by the level of reproduction in muri ne lungs and by immunogenicity. Strains with genomic formulas 6/2 (HA and NA of a virulent strain) and 5/3 (M) (HA, NA, and M of a virulent strain) were characterized by the highest immunogenicity. Reassortants including, besides HA and NA, PA gene 5/3 (PA) or inheriting only HA gene from strain A/pr/8/34 (H1N1) were hyperattenuated and immunogenic .