Twenty-seven years experience with immunogenicity of inactivated influenza vaccines in the elderly

Introduction: Influenza vaccination of elderly people is efficacious and cost effective for the prevention of influenza and its complications, but generally elderly respond suboptimally to influenza vaccination because of the presence of comorbidities and immunosenescence. The aim of our study was to examine the immunogenicity of influenza vaccines in subjects aged over 60, focusing on the weight that some factors, i.e. age (60-84 and ≥85), sex, or type of vaccines, may have on the antibody response. We analysed the data obtained by our research group in 27 winter seasons (from 1988-1989 to 2014-2015), in 4,461 elderly people, most of them with underlying medical conditions, vaccinated with different commercially available seasonal trivalent inactivated influenza vaccines. Materials and Methods: The antibody response was examined comparing haemagglutination inhibition antibody titers in sera collected before and 30 days after vaccination.and post-vaccination results were evaluated according to the criteria of the Committee for Medicinal Products for Human Use (CHMP) for approval of influenza vaccines. All statistical analyses to compare the different subgroups were carried out using Matlab® of MathWorks Inc. release 2014b. Results: Responses in most instances satisfied at least one of the 3 CHMP criteria. Higher responses were found against A/H3N2 vaccine components in female as compared with male subjects. The response in elderly (60-84y) and very elderly (≥85y) was in most instances similar, in both age groups the difference between males and females was still observed. The two enhanced vaccines used, MF59-adjuvanted and intradermal, induced similar and higher responses compared with conventional vaccines against A/H3N2 antigen. Against A/H1N1, the response induced by MF59-adjuvanted vaccine was in most instances higher than conventional and intradermal vaccines, whereas against B antigen, intradermal vaccine induced higher HI response than that induced by conventional and MF59-adjuvanted vaccines. Conclusions: Our data evidenced that the use of influenza vaccination appear to be an appropriate strategy to address the challenge of influenza infections of the elderly. Moreover they underline the necessity to expand researches and approaches to understand immunosenescence and its relationship to vaccine-induced immunity in order to have more valid vaccines. The vaccine induced stimulation of HI antibody response following vaccination was found to be influenced by different factors as age, sex and type of vaccine. It is therefore important to understand the mechanisms that result in these differences and to use such information to devise more immunogenic influenza vaccine candidates.