Antigenic analysis of influenza viruses isolated in Thailand between 1991 and 1994.

We studied the epidemiology of influenza viruses in Thailand by isolating them and comparing their antigenic features with those of Japanese isolates. Between 1991 and 1994, 32 strains were isolated from 186 throat swab specimens. Twenty-one of the 32 isolates were of type A, subtype H3N2, and 11 strains were type B. It was suggested that the isolates of type A, subtype H3N2, drifted antigenically from A/Beijing/352/89-like to A/Kitakyusyu/159/93-like variants used as reference strains for comparison. The type B isolates in 1991 were suspected to be antigenically different from those of B/Bangkok/163/90, Thailand, in HI tests. These 1991 isolates were similar to B/Mie/1/93, which was isolated in the latter half of the epidemic in Japan in winter 1992/1993.