Immunogenicity and safety of a recombinant adenovirus type-5 COVID-19 vaccine in adults: data from a randomised, double-blind, placebo-controlled, single-dose, phase 3 trial in Russia

Background To determine the immunogenicity, efficacy, reactogenicity, and safety of a single dose of recombinant adenovirus type-5 vectored COVID-19 vaccine (Ad5-nCoV, 5 × 1010 viral particles per 0.5 mL dose), we conducted a single-dose, randomised, double-blind, placebo-controlled, parallel group (3:1 Ad5-nCoV:placebo), phase 3 trial (Prometheus). Methods From 11-September-2020 to 05-May-2021, across six sites in the Russian Federation, 496 participants were injected with either placebo or Ad5-nCoV expressing the full-length spike (S) protein from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Results Seroconversion (the primary endpoint) rates of 78.5% (95% CI: 73.9; 82.6) against receptor binding domain (RBD), 90.6% (95% CI: 87.2; 93.4) against S protein and 59% (95% CI: 53.3; 64.6) against neutralising SARS-CoV2 antibodies 28 days post-vaccination. Geometric mean titres (GMTs) were also elevated for antibodies against the RBD (405.32 [95% CI: 361.58; 454.46]) and S protein (678.86 [95% CI: 607.44; 754.40]) compared to the GMT of neutralising antibodies against SARS-CoV-2 (16.73 [95% CI: 15.36; 18.22]). Using an IFN-γ ELISpot assay after stimulating the cells with full-length S protein we showed that the Ad5-nCoV vaccine induced the most robust cellular immune response on Days 14 and 28. Up to Day 28, the primary and all secondary endpoints of the Ad5-nCoV vaccine were statistically superior to the placebo (р <0.001). Systemic reactions were reported in 113 of 496 (22.8%) participants (Ad5-nCoV, 26.9%; Placebo, 10.5%), and local reactions were reported in 108 (21.8%) participants (Ad5-nCoV, 28.5%; Placebo, 1.6%). These were generally mild and resolved within 7 days after vaccination. Of the six serious adverse events reported, none of the events were vaccine related. There were no deaths or premature withdrawals. Conclusion A single-dose of Ad5-nCoV vaccine induced a marked specific humoral and cellular immune response with a favourable safety profile. Trial Registration ClinicalTrials.gov: [NCT04540419][1] ### Competing Interest Statement The authors of this manuscript have the following competing interests: MT, MK, DZ, AA, NK, AT and VD are employees of NPO Petrovax Pharm LLC. TZ and LB are employees of CanSino Biologics, Inc. IA, SS, KZ and YS have received funding from NPO Petrovax Pharm LLC for consultation services. DL and GE have received personal fees from NPO Petrovax Pharm LLC for consultation services. ### Clinical Trial NCT04540419 ### Funding Statement The study was funded by NPO Petrovax Pharm LLC (Moscow, Russian Federation). NPO Petrovax Pharm LLC in partnership with CanSino Biologics, Inc. (Tianjin, China) are funding and managing the clinical development of the Ad5-nCoV vaccine in the Russian Federation. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Independent Ethics Committees of the involved sites and the Ethics Council of the Ministry of Health of the Russian Federation gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present work are contained in the manuscript and supplmentary materials [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT04540419&atom=%2Fmedrxiv%2Fearly%2F2022%2F03%2F11%2F2022.03.01.22271507.atom