Safety and immunogenicity of intranasally administered inactivated trivalent virosome-formulated influenza vaccine containing Escherichia coli heat-labile toxin as a mucosal adjuvant

A trivalent influenza virosome vaccine containing hemagglutinin and Escherichia coli heat-labile toxin (HLT) was administered intranasally to young adults and elderly subjects. Symptoms that followed immunization were mild and transient. A significant increase in serum hemagglutination inhibition (HI) antibody was noted for the 3 vaccine strains. There was no significant difference in postimmunization geometric mean titers or seroconversion rates between age groups. The percentage of subjects attaining protective HI titers (greater than or equal to 40%) was comparable in both groups for the A/Bayern (P = .5) and B/Beijing (P = .3) strains but was higher among young adults (92.2%) versus elderly subjects (76.5%; P = .057) for the A/Wuhan strain. The proportion of subjects with nonprotective baseline titers who attained protective levels after immunization was similar in both age groups for the A/Bayern and B/Beijing components, For the A/Wuhan component, significantly (P = .017) more young adults achieved protective titers versus elderly subjects (85.7% and 53.8%, respectively). Vaccination evoked a significant (P < .005) increase in anti-HLT antibody titers.