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Vaccine Coverage and Hesitancy · Journal article
The Journal of Immunology · July 28, 2026
Well-designed and adequately powered for the question it asks.
This randomized controlled trial (Chrono-Vax) demonstrates that morning influenza vaccination (9:00-11:40) produces significantly greater antibody responses compared to afternoon vaccination in adults aged 60-85 years. While a similar trend was observed for T-cell responses, this did not reach statistical significance. The findings support time-of-day optimization of influenza vaccination in older adults.
Randomized controlled trial. Adults aged 60-85 years. Intervention: Influenza vaccination administered at morning time window (9:00-11:40). Compared with: Influenza vaccination administered at early afternoon (11:40-14:20) or late afternoon (14:20-17:00).
Morning vaccination (9:00-11:40) elicited significantly greater fold increase in antibody titers versus 11:40-14:20 time window (p = 0.005) Morning vaccination (9:00-11:40) elicited significantly greater fold increase in antibody titers versus 14:20-17:00 time window (p = 0.009) Generalized additive mixed model showed significant effect of vaccination timing on antibody response (p = 0.012) with strongest response estimated at 9:00
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Morning vaccination scheduling (9:00-11:00) may be preferred for influenza vaccination in older adults to optimize antibody responses and potentially improve protection against severe disease, though the clinical magnitude of benefit and generalizability to other populations requires confirmation.
Randomized controlled trial with pre-specified primary endpoints (antibody and T-cell responses) in a well-defined older adult population shows statistically significant morning vaccination advantage, though T-cell effect did not reach significance.
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Quoted from the source exactly as published.
Morning vaccination scheduling (9:00-11:00) may be preferred for influenza vaccination in older adults to optimize antibody responses and potentially improve protection against severe disease, though the clinical magnitude of benefit and generalizability to other populations requires confirmation.
Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.
Abstract Introduction 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. Funding Source This abstract is part of the BioClock Consortium (with project number 1292.19.077) of the research program NWA-ORC, which is (partly) financed by the Dutch Research Council (NWO). Additional funding was received from the Dutch Ministry of Health, Welfare Topic Categories Translational and Interventional Immunology (TI)
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