EXTENT OF ANTIGENIC VARIATION OF A2 INFLUENZA VIRUSES FROM PROTOTYPE STRAINS.

Summary Application of the cell culture neutralization (N) test demonstrates that representative strains of the 1963 A 2 variant are antigenically homogeneous. Reaction patterns of individual antisera clearly show the differences between the 1957 strain and the current family of A 2 viruses. None of these differences could be demonstrated by hemagglutination-inhibiting (HI) test alone. The analysis of the patterns of incidence of N antibody in recruit populations lends laboratory support to the epidemiologic descriptions of the progression of the 1963 epidemic across the United States. Despite the presence of considerable N antibody to both the 1957 and 1963 strains of virus, 47 cases of A 2 virus infection were confirmed in 1963. The tenuous correlation between humoral antibody to influenza and immunity has been discussed.