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Influenza virus subunit vaccines. II. Immunogenicity and original antigenic sin in humans.

Subunit vaccines containing hemagglutinin, neuraminidase, and nucleocapsids of A/Port Chalmers/1/73 (H3N2) influenza virus were prepared after treatment of purified virus with ammonium deoxycholate. The immunogenicity of these subunits and the response to the common and specific antigenic determinants on the hemagglutinin subunits were studied in man. The subunits were as immunogenic in man as intact inactivated influenza virus vaccine at an equivalent concentration. Booster doses of antigen did not increase the antibody responses. Intact influenza B virus vaccine did not potentiate the immune response to the type A subunits in man. Volunteers responded differently to the common and specific determinants on the hemagglutinin subunits. The predominant antibody response was to the common or cross-reacting determinants present on hemagglutinins of both A/Hong Kong/1/68 (H3N2) and Port Chalmers/73 virus. Some men who failed to produce specific antibodies to the hemagglutinin of Port Chalmers/73 virus responded to the specific determinants on the Hong Kong/68 hemagglutinin. Higher doses of the subunit vaccines (1,400 chick cell-agglutinating units) did induce antibodies to the specific determinants on the Port Chalmers/73 virus hemagglutinin as well as to the common and specific determinants on Hong Kong/68 influenza virus.