Evaluation of the efficacy of split-product trivalent A(H1N1), A(H3N2) and B influenza vaccine

The efficacy of split-product trivalent A(H1N1), A(H3N2) and B influenza vaccine in primary school childlen aged seven to 12 years was studied during 1980-1984. This vaccine was adequately immunogenic with infrequent reactions. Hemagglutination inhibition (HAI) antibody responses to A (H3N2) virus were the most excellent among the components. The incidence of confirmed infection of the vaccinees were 6.5 % to 34.8% lower than those of the non-vaccinees in either years. As the result, the efficacy of vaccine was recognized (x^2 = 76.34, p < 0.001). However, this was not recognized in an entrant school's epidemic in 1984 caused by intense antigenic drift strain. The protective level of HAI antibody titer was 256, but increased to 521 in 1984 epidemic reflecting the high rate of isolates with intense antigenic drift