Influenza Vaccine Immunogenicity in Hemodialysis Patients

<b>Background:</b> Patients with end-stage renal disease (ESRD) on hemodialysis are at increased risk for severe influenza, and underlying immune dysfunction may limit vaccine-induced protection. <b>Methods:</b> This observational open-label study evaluated immune responses in 93 hemodialysis patients vaccinated with seasonal inactivated influenza vaccine (IIV) during the 2019-2020 (n = 22) and 2023-2024 (n = 71) seasons. Immune responses were comprehensively assessed using hemagglutination inhibition and microneutralization assays to measure antibody levels, together with flow cytometry analysis of key immune cell populations, including plasmablasts, T-follicular helper cells (Tfh), and effector memory T cells (Tem). <b>Results:</b> During the 2019-2020 season, antibody responses in hemodialysis patients were comparable to those in healthy volunteers in both younger (18-60 years) and older (over 60) age groups. By day 7 post-vaccination, there was a pronounced increase in activated Tfh1 cells, coinciding with a surge in plasmablasts and a rise in antigen-specific B cells. This was accompanied by a T-cell response mediated by IFNγ-producing and polyfunctional CD4+ Tem cells. In the 2023-2024 season, revaccination was associated with higher baseline antibody levels but did not alter subsequent response kinetics to A/H1N1pdm, A/H3N2, and B/Yamagata antigens. In contrast, responses to B/Victoria were higher in revaccinated patients throughout the entire observation period. <b>Conclusions:</b> Our findings confirm that standard-dose IIV vaccination is beneficial for hemodialysis patients, inducing robust and adequate humoral and T-cell immune responses.