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Laboratory-based surveillance of influenza A(H1N1) and A(H3N2) viruses in 1980-81: antigenic and genomic analyses.

During 1981, the A/Brazil/11/78-like strains of influenza virus that had been prevalent from 1978 to 1980 were displaced by a new set of heterogeneous, but closely related, variants (reference strain, A/England/333/80). Genomic analysis revealed that these new variants were almost exclusively nonrecombinant H1N1 viruses, i.e., they contained no genes of H3N2 origin. However, a few recombinant viruses containing the new variant HA and genes of H3N2 origin were identified. Antigenic analysis of H3N2 viruses indicated that they were also heterogeneous. The majority of these virus isolates were antigenically intermediate between A/Texas/1/77 and A/Bangkok/1/79, but additional variants were detected. Genomic analysis revealed that the H3N2 viruses isolated in the winter of 1980-81 were quite similar to H3N2 viruses isolated from 1977-79 in their T(1) oligonucleotide maps. No H1N1 genes were detected in H3N2 virus isolates. Comparison of pairs of oligonucleotide maps of total virus RNA indicated that a similar rate of genetic change had occurred for nonrecombinant H1N1 viruses, for recombinant H1N1 viruses, and for H3N2 viruses and that, in general, pairs of viruses exhibited increasing numbers of changes in their oligonucleotide maps as the time interval between isolation of the viruses increased.