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 Escheri chia coli heat-labile toxin (HLT) was administered intranasally to young ad ults and elderly subjects. Symptoms that followed immunization were mild an d transient. A significant increase in serum hemagglutination inhibition (H I) antibody was noted for the 3 vaccine strains. There was no significant d ifference in postimmunization geometric mean titers or seroconversion rates between age groups. The percentage of subjects attaining protective HI tit ers (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 a dults (92.2%) versus elderly subjects (76.5%; P = .057) for the A/Wuhan str ain. The proportion of subjects with nonprotective baseline titers who atta ined protective levels after immunization was similar in both age groups fo r the A/Bayern and B/Beijing components, For the A/Wuhan component, signifi cantly (P = .017) more young adults achieved protective titers versus elder ly subjects (85.7% and 53.8%, respectively). Vaccination evoked a significa nt (P < .005) increase in anti-HLT antibody titers.