Immunogenicity and safety of three commercial influenza vaccines in institutionalized elderly

Influenza is a leading cause of morbidity and mortality in elderly people. This prospective, observed-blind, randomized, multicenter trial compares the immunogenicity and safety of three influenza vaccines in a sample of 635 elderly residents of four nursing homes in Milano (Italy). All vaccines were well tolerated: no serious adverse events were recorded, and a small number (9 subjects) of local and systemic reactions were observed. Twenty-nine oropharyngeal swabs were taken during the season from ILI (influenza-like illness) patients, none of whom was positive for influenza and other respiratory viruses. Immunogenicity was evaluated in a subgroup of 111 subjects with blood samples obtained just before vaccination and after 4 and 12 weeks. The adjuvanted vaccines, subunit vaccine with MF59 (a-SUV) and virosome subunit vaccine (v-SUV), induced a higher antibody response than whole virus vaccine (WVV). There was no significant difference between groups that received a-SUV and v-SUV, but the a-SUV group had higher values of geometric mean titres than the v-SUV group for H1N1 and B influenza strains. These findings suggest that influenza vaccination is effective, and they underscore the importance of vaccination programs for institutionalized elderly. Further studies are needed to compare other adjuvanted vaccines in order to define their different properties.