Evaluation of Immune Responses to seasonal influenza vaccination in healthy volunteers in south Apulia, Italy: a pilot study

Background: The aim of our pilot study is to investigate different components of the immune response to influenza vaccination in a group of healthy volunteers. We evaluated the cellular immune response (CD4+ T lymphocytes) by flow cytometry. The humoral immune response was assessed by measuring the serum haemagglutination inhibition antibody response. Methods: Healthy adult donors (n = 18), were vaccinated with a commercially influenza virus vaccine (FLUARIX® GlaxoSmithKline S.p.a. Verona, Italy), peripheral blood was drawn the same day as influenza virus vaccination and one month later in order to enumerate the antigen-specific CD4+ T lymphocytes. Hemagglutination inhibition assay was performed to enumerate the titer of neutralizing antibodies. Samples of nasal-pharyngeal secretions were taken by swabbing, from ILI (Influenza like Illness) subjects among the studied group, in order to verify influenza infections and eventually identify viruses using Real Time PCR. Results and Conclusions: Parenteral influenza vaccination results in significant increase in the CD4+ Th cell population after vaccination. The number of pre-vaccination CD4+ T cells was 0.018 [the results are presented as number of percent fluorescent cells per 10 000 lymphocytes (fixed cells)], while there was a significantly higher number of CD4+ Th cells one month after vaccination (statistical significance was set at the level of α = 0.01). Twenty-two percent of patients demonstrated protective antibody levels to influenza A H1/N1 serotype. None was diagnosed with influenza type A or B.