Antibody Response to the Hong Kong Strain of Influenza A2 Virus in Paired Sera Collected from Influenza Patients in 1965 to 1969

Abstract

Hemagglutination-inhibiting (HI) antibody response to influenza A2/Singapore/1/57, A2/Finland/1/65 and A2/England/334/68 (Hong Kong) was studied in 3 identical groups of influenza patients from the epidemics of 1965, 1968 and 1969. Each group of samples consisted of 26 serum pairs with a significant rise in the complement-fixing antibody titer. 73 and 85% of the patients from the 1965 and 1968 epidemics, respectively, had antibodies to the Hong Kong strain in their acute phase sera. 81% of the 1969 serum pairs showed an HI antibody increase to the Hong Kong strain as compared to 39% in the paired sera from the two previous epidemics. About 50% of the 1969 patients showed an increase in the HI titer against the two earlier strains. The mean HI titers against the Hong Kong strain remained in all groups lower than the titers against the two other strains used.