Antigenic Variants ~ Antibody

Antigenic variation in influenza viruses isolated from man has been recognized since 1936 (1--4). Recent elaborate investigations of the antigenic composition of Type A and A-prime viruses and of Type B isolates have provided much additional information. These data outline the antigenic relationships of strains of virus isolated in various years and at various places (5-8). In general it appears that many antigens are shared among strains of a type of virus and that the serologic specificity of a strain is conferred by a dominance of one or more of these antigens (2, 3, 9). The dominant antigens of influenza virus tend to change. Nevertheless, there is little information about the effects of repeated natural exposure to antigenic variants of influenza viruses upon the antibody content and acquired immunity of the population at large. There are, however, certain observations concerning the relation between antigenic variation, antibody content, and immunity. For example, the epidemic of influenza A-prime which occurred in 1947 was followed by a proportionately greater increase in antibody in young adults to the new strain than to PR8, although the final level of antibody to the latter was the higher (10). Vaccination with the older strain, while stimulating good titers of antibody to the PR8 strain, failed, with respect to the new strain, to stimulate significant antibody or protection. In addition, it has been noted that the sera of children, who constitute the most susceptible portion of the population, now ordinarily contain A-prime antibodies (11) rather than, as formerly, antibodies against Type A strains of virus (12).