Statistical Analysis
ADVERSE EVENT
The sample size was calculated to be approximately 18 000 participants in cohort 1 (vaccine: 14 400, placebo: 3600) and 6000 in cohort 2 (vaccine: 4800, placebo: 1200) (eMethods in Seroconversion was defined as a 4-fold increase in anti–SARS-CoV-2 S1 IgG titer compared with the baseline. Adverse events were compared between the vaccine and placebo groups using the χ