Background Emerging evidence suggests that the time in the day of vaccination may influence post-vaccination immunogenicity. The main objective of this study was to assess the association between the time of vaccination and the anti-EBOV GP 1,2 IgG antibody response at 12 mo following vaccination against Ebola virus disease (EVD). Methodology/Principal Findings This study utilized data from a randomized, double-blind, placebo-controlled international phase 2b clinical trial (PREVAC) evaluating the immunogenicity of three vaccination strategies against Ebola virus disease (rVSVΔG-ZEBOV-GP one and two doses, and Ad26.ZEBOV/MVA-BN-Filo) in 1,859 healthy Western Africans. In the overall population, we measured a statistically significant association between the time of day of first vaccination and anti-Ebola virus immunoglobulin G levels at 12 mo ( p = 0.02). The magnitude of this association was small, participants vaccinated at 1600 h were estimated to have 1–7% lower antibody levels at 12 mo compared to those vaccinated at 1000 h. Conclusions/Significance An effect of the time of first vaccination on the antibody responses was found but remains modest and unlikely to impact the EVD vaccine effectiveness. Clinical Trials Registration ClinicalTrials.gov registration: NCT02876328 .
Kpetigo et al. (2026) studied this question.