Clinical experience with inactivated, virosomal influenza vaccine

Current available influenza vaccines are safe and effective in preventing influenza. Nevertheless, there is a need for influenza vaccines with improved efficacy in the elderly. This need is underscored by both the observation that influenza has a major clinical and economic impact in the elderly and the fact that currently available vaccines are generally less effective in elderly than in younger subjects. Several approaches are currently being pursued in order to improve the efficacy of influenza vaccines in elderly individuals and others who have impaired immune responses to conventional influenza vaccines. A novel antigen-presenting strategy to overcome impaired immune responses is the use of virosomes. Previously, data on safety and reactogenicity have been published regarding the use of virosomal influenza vaccines. Data from three recent clinical trials are presented here. The first of these was a comparative study of a virosomal vaccine and a conventional subunit vaccine in "at-risk" adults with underlying chronic illness. The virosomal vaccine demonstrated comparable tolerability to the subunit vaccine, with about 98% of patients reporting tolerability to be good or very good. The vast majority of adverse events reported were mild to moderate in severity. With both vaccine types, mean HI titres decreased with age for both the A-H1N1 and B influenza virus strains, but for the A-H3N2 strain (the most virulent of the three strains), mean HI titres did not decrease with age, suggesting a better response with the virosomal vaccine when compared to the subunit vaccine. All three studies explored the long-term persistence of antibodies after vaccination with virosomal influenza vaccines. Immunogenicity declined over time but remained high at 4, 6 and 12 months post-vaccination compared to baseline, indicating that adequate seroprotection is achievable for the duration of the influenza season. Virosomal vaccines may induce better immunity in elderly subjects and may be more effective in reducing morbidity and mortality in this age group.