PhD Candidate Dutch National Institute for Public Health and the Environment Bilthoven, Utrecht, Netherlands
Disclosure(s):
Tamara Brouwers, MSc: No financial relationships to disclose
Introduction/Rationale: Increasing evidence suggests that timing of vaccine administration affects immune responses, with some studies indicating that morning influenza vaccination (9:00-11:00) elicits a stronger antibody response than afternoon vaccination (15:00-17:00) in older adults. Existing trials focused on antibody responses, but did not assess induction of T-cell responses, which are also crucial for immunity to respiratory viruses and may contribute to time-of-day dependent vaccine effects.
Methods: Here, we analyzed data from the randomized controlled trial Chrono-Vax to determine the effect of influenza vaccination time on immune responses across a continuous time window from 9:00-17:00 in adults aged 60-85 years. Antigen-specific antibody titers and T-cell responses were measured before and one month after vaccination against three vaccine strains (A/H1N1, A/H3N2, and B/Victoria) with the hemagglutination inhibition and IFN-γ ELISpot assay, respectively.
Results: Antibody responses between the three randomized vaccination time groups (9:00-11:40, 11:40-14:20, 14:20-17:00) were compared using linear mixed effects models adjusted for baseline antibody titers. Vaccine strain-specific antibody responses were jointly analyzed within a single mixed-effects framework. Morning vaccination (9:00-11:40) resulted in a significantly greater fold increase in antibody titers than early and late afternoon vaccination (11:40-14:20, p = 0.005; 14:20-17:00, p = 0.009). Additionally, a generalized additive mixed model showed a significant effect of influenza vaccination timing on the antibody response (p = 0.012), with the strongest response estimated at 9:00. A similar pattern was observed for influenza-specific T-cell responses, though this effect did not reach statistical significance.
Conclusion: In summary, our findings indicate that morning influenza vaccination can enhance antibody responses in older adults, suggesting that tailored vaccination timing may improve protection against severe disease in this population.
