Origin and evolutionary characteristics of antigenic reassortant influenza A (H1N2) viruses isolated from man in China.

During the 1988/1989 influenza season, five antigenic reassortant influenza A (H1N2) viruses not previously isolated from man were isolated in Hebei province, People's Republic of China. All isolates contained haemagglutinins (HAs) and neuraminidases (NAs) which were antigenically similar to those of the recent Russian (H1N1) and Hong Kong influenza A (H3N2) viruses, respectively. The results of antigenic and nucleotide sequence analyses revealed that the genes encoding the polymerase, nucleoprotein, NA, matrix and non-structural proteins of the reassortant A/Hebei/24/89 (H1N2) virus were derived from the H3N2 parent virus, whereas its HA gene was from the H1N1 parent virus. The nucleotide sequences of the HA (encoding the HA1 subunit) and NA genes of the reassortant viruses were also determined. Phylogenetic trees constructed from these data by the neighbour-joining method revealed that the HA gene of the reassortant virus was closely related to those of recent human H1N1 viruses, whereas the NA gene was related to a recent human Hong Kong (H3N2) virus lineage.