Inactivated influenza vaccine efficacy: diminished antigenicity of split product vaccines in mice

Abstract

Groups of 60 to 120 mice were given a single intraperitoneal inoculation of varying dilutions of commercially prepared and licensed bivalent (A/England and B/Mass) and monovalent (A/Aichi or B/Hong Kong) inactivated influenza vaccines, and their antibody responses at 14 days were quantitated by hemagglutination inhibition tests. Split product vaccines prepared by the treatment of A/England, B/Mass, and B/Hong Kong whole virus with Tween 80 and either tributylphosphate or ether produced significantly lower mean antibody titers than did equivalent whole virus preparations. The rates of seroconversion (< 1:8 to ≥ 1:8) at the various dilutions tested were also significantly reduced when these split product vaccines were given. When the antigen content of all vaccines was quantitated by the chick cell agglutination test, between 10 and 100 times more split product antigen than whole virus antigen was required to produce seroconversion in 50% of the mice tested. Differences between split product and whole virus A/Aichi vaccines were less marked. These data stress the need to consider factors other than hemagglutinin content alone in determining the immunogenicity of inactivated influenza vaccines.