Ether-treated, subunit Hsw1N1 influenza vaccines: response of immunologically primed subjects to two antigenic variants.

Two bivalent, ether-treated, subunit influenza vaccines were compared in adults greater than or equal to 45 years old. Both vaccines contained 200 chick cell-agglutinating (CCA) units of A/Victoria/3/75 antigen/dose. The Hsw1N1 components, also at a level of 200 CCA units/dose and designated A/Shope and A/X-53, were antigenically representative of the A/swine/1976/31 and A/New Jersey/8/76 viruses, respectively. A/Shope virus possessed about 100 times more neuraminidase activity than A/X-53 virus. The two vaccine groups had equivalent geometric mean titers (GMTs) of antibody to A/NJ virus, with about 95% of each group having titers of greater than or equal to 1:40 after vaccination. Group GMTs of antibody to A/Vic virus were also equivalent. Failure of the A/X-53 vaccinees to respond according to the dogma of original antigenic sin and a highly significant between-group difference in response to A/PR/8/34 antigen are interpreted as due to a difference in vaccine neuraminidase levels. It is suggested that, although A/Shope was as serologically effective against A/NJ virus as A/X-53 in this age group, under similar conditions a recombinant with the A/NJ hemagglutinin and the stable A/swine neuraminidase antigens might be more effective against A/NJ than either of the present vaccines.