Randomized Placebo-Controlled Trial of Ad5-nCoV Vaccine

The investigational vaccine, Ad5-nCoV, and the placebo were provided by NPO Petrovax Pharm LLC (Moscow, Russia). Both vaccine and placebo were developed by CanSino Biologics Inc. (Tianjin, China) and the Beijing Institute of Biotechnology (Beijing, China). The vaccine was administered with the optimal dose of 5 × 10¹⁰ viral particles per 0.5 mL dose, as determined in a previous study [9 (link),10 (link)]; placebo contained vaccine excipients only. The appearance of Ad5-nCoV and placebo syringes and packaging was identical.
Eligible participants were randomly allocated to the Ad5-nCoV group or the Placebo group, in a 3:1 ratio, by an independent statistician using a validated system including a pseudorandom number generator with a seed value; allocation used block randomisation and stratification by study site. Neither the investigators nor participants were aware of the group assignment. Investigators were trained to use the centralised interactive web response system that was used for randomisation. Randomisation codes were kept by authorised personnel from the responsible contracted organisation.
The Safety Analysis Set included all randomised participants who received a dose of the vaccine and was used to provide the disposition of study participants. Results for immunogenicity analyses are presented for the full analysis set ([FAS] for immunogenicity analysis), which included all eligible participants who received a dose of vaccine and provided at least one immunogenicity assessment result. The study design (S1 Protocol) also included the per-protocol sets ([PPS] for immunogenicity analysis and PPS efficacy analysis), which included members of the FAS for immunogenicity analysis and Safety Analysis Set, respectively, with no significant protocol deviations and who did not develop COVID-19 within the first 14 days post-vaccination. The population characteristics and results were similar between the FAS for immunogenicity analysis and both types of PPS (immunogenicity and efficacy analysis); therefore, only the FAS for immunogenicity analysis population was used to evaluate the immunogenicity endpoints in this study. Cellular immunity results were analysed in a subset of participants from the FAS for immunogenicity analysis population that attended the Moscow clinic site (n = 69). Details describing the sample sizes are provided in S1 Methods.