EFFICACY OF PURIFIED INFLUENZA SUBUNIT VACCINES AND RELATION TO THE MAJOR ANTIGENIC DETERMINANTS ON THE HEMAGGLUTININ MOLECULE

Inactivated whole-virus vaccine of influenza A/Scotland/74 (H3N2) virus containing 700 or 1, 400 chick cell-agglutinating (CCA) units, a purified subunit vaccine of equivalent dosage, or placebo were studied in 186 adult volunteers. Placebo was least reac-togenic, 1, 400-CCA unit whole-virus vaccine was most reactogenic, and others were intermediate. Vaccines were equally antigenic, and delineation of antibody specificities revealed antibody cross-reacting with A/Hong Kong/68 (H3N2) virus in all sera. Antibody specific for A/Hong Kong/68 virus was found in 82% of sera and for A/Scotland/74 virus in 46%. When compared with volunteers given placebo, volunteers given 700 CCA units of subunit or whole-virus vaccine exhibited significant protection against infection with live A/Scotland/74 virus. Infections in vaccinees occurred only in those with low titers of antibody to A/Scotland/74 virus, and this antibody was of the cross-reacting type. Persons with moderate and high levels of antibody resisted infection regardless of the absence or presence of antibody specific for A/Scotland/74 virus. Purified subunit vaccines provide an alternative to whole-virus preparations in primed individuals. Efficacy of vaccines may be dependent on the nature of the antibody response. © 1979 by The University of Chicago.