Randomisation and masking
All enrolled participants were randomly assigned (1:1) to receive two doses of either the dNS1-RBD vaccine or placebo. Block randomisation was done at each study centre by trained blinded investigators using an interactive web-response system, stratified according to centre, age group (18–59 years or ≥60 years), and the presence or absence of any previous SARS-CoV-2 vaccination. The unblinded statistician from the contract research organisation (Hangzhou Tigermed Consulting, Hangzhou, China) who designed the randomisation plan and generated the block randomisation codes was not involved further in the trial.The vaccine and placebo were identical in appearance. To prevent cross-contamination between the vaccine and placebo groups during administration, which has been reported previously,