Time of day of vaccination does not influence antibody responses to pneumococcal and annual influenza vaccination in a cohort of healthy older adults.

Vaccines are less immunogenic in older adults, partly due to immunosenescence. Having previously shown that morning influenza vaccination may be more immunogenic in older adults (mean age 71), we assessed if this could be replicated in a younger cohort (mean age 57) and with a T-cell independent vaccine. This study examined whether diurnal timing of a single dose of Pneumovax® (PPV-23) and seasonal influenza vaccine influenced antibody responses in 140 healthy adults over the age of 50. Pneumococcal serotype-specific (PnPS) antibodies and Haemagglutination Inhibition Assays (HAI) were used to characterize antibody responses at Baseline, 1, 4, and 52 weeks post-vaccination. Protective thresholds were set at 0.35 μg/mL for two-thirds of PnPS tested (WHO≥8/12PnPS) and a titre of ≥40 HAI for H1N1, H3N2, and B/Victoria strains. Both AM and PM cohorts showed increased Pn-specific antibodies to one PPV-23 dose at weeks 1, 4, and 52; however, time of day did not significantly influence antibody responses. Baseline immunity for pneumococcus was high (57.1 % AM, 50.0 % PM had WHO≥8/12PnPS), and immunity was maintained with at least 7/12 serotypes elevated at 52 weeks. Time of day did not alter short- or long-term influenza antibody responses. H1N1 had the highest baseline immunity (67.6 % AM, 48.6 % PM had ≥40 HAI) and the most increased responses at week 4 post-vaccination (92.8 % AM, 94.1 % PM) that were maintained at 52 weeks post-vaccination (91.7 % AM, 89.3 % PM). The poorest serotype immunity was for the B/Victoria strain at all time points. Although time of day did not influence vaccine immunogenicity in AM and PM cohorts, sustained cohort-wide antibody responses were demonstrated in an older population. Identifying 18 % of the total cohort exhibited suboptimal responses to pneumococcal or influenza vaccines underscores the imperative for enhancing vaccine efficacy within this age group to reduce morbidity and mortality.