Statistical analysis and sample size determination
Since this is a first-in-human dose-escalation single-dose Phase I study of 2 vaccines, the statistical analysis did not include formal hypothesis testing and therefore the sample size calculation was not based on statistical power. Group sizes were based on regulatory precedent. Accordingly, all analyses were descriptive, and no hypotheses were formally tested. All analyses included all randomised participants who took at least one dose of study vaccine or placebo. Confidence intervals (CIs) were calculated at the two-sided 95% level based on the t-distribution on the log base 10 transformed values, then back transformed (power of 10) on the original scale. Antibody titres were logarithmically transformed (base 10) and the geometric mean fold rise (GMFR) comparing the relative change in the geometric mean level at day 29 post-vaccination (and in some cases at day 8 as well) compared to baseline presented for each vaccine dosing and placebo group. Statistical analyses were performed using Stata version 16.1 and R version 4.2.2.