Head-to-head comparison of four nonadjuvanted inactivated cell culture-derived influenza vaccines: effect of composition, spatial organization and immunization route on the immunogenicity in a murine challenge model

In order to study the influence of antigen composition, spatial organization of antigen and the route of administration, four cell culture-derived, inactivated, nonadjuvanted influenza vaccine formulations, i.e. whole inactivated virus (WIV), split, subunit and virosome vaccines were prepared from a single antigen batch. We directly compared the immunogenicity and efficacy of these vaccine formulations after intramuscular (i.m.) or intranasal (i.n.) administration in mice. Prime and boost vaccination were followed by a potentially lethal homologous aerosol challenge. For all vaccines, the i.m. route induced higher serum humoral immune responses as compared to the i.n. route and protected all mice against challenge at a dose of 5 microg. Upon i.n. immunization only WIV and split vaccines induced detectable IgG titers and partial protection against challenge but only very low HI titers were induced in almost all mice. WIV induced mainly IgG2a/c titers via both routes, whereas split vaccine induced exclusively IgG1 titers via both routes. Subunit and virosome vaccines induced exclusively IgG1 via the i.m. route. Mucosal sIgA levels were only detected after i.n. vaccination with WIV. Furthermore, vaccines containing all viral components (WIV and split vaccine) induced higher serum HI titers and serum antibody titers than subunit and virosome vaccines. The differences in magnitude and quality of immune responses of split and WIV, having the same composition, are likely related to their distinct spatial organization. In conclusion, the direct comparison between WIV, split, subunit and virosomes, shows that the differences in immune responses between these well known influenza vaccines can be explained by both the composition and particulate structure of these vaccine formulations.