ANALYSIS OF INFLUENZA-A VIRUS REINFECTION IN CHILDREN IN JAPAN DURING1983-91

The epidemiology of influenza A in Japan was studied during 1979-91 an d viruses isolated from reinfections during 1983-91 were analysed. Of 2963 influenza viruses isolated during this period, 922 and 1006 were influenza A(H1N1) and A(H3N2) viruses respectively; the others were in fluenza B viruses. Influenza A(H1N1) and A(H3N2) caused 5 and 6 epidem ics respectively, most accompanied by antigenic drift. Seventeen reinf ections with H1N1 and 17 with H3N2 were detected during our study. Til e primary and reinfection strains isolated from 7 H1N1 and 10 H3N2 cas es were studied by haemagglutination-inhibition, and amino acid and nu cleotide sequences of the HA1 region of the haemagglutinin, Most of th e primary and reinfection strains mere antigenically and genetically s imilar to the epidemic viruses circulating at that time. However, in 4 out of 10 cases of reinfection with influenza H3N2 virus, reinfection strains mere genetically different from the epidemic viruses.