We present the results of a randomized, double-blind, placebo-controlled, multi-center clinical trial of the tolerability, safety, and immunogenicity of the inactivated whole virion concentrated purified coronavirus vaccine CoviVac in adult volunteers aged 18-60. Safety of the vaccine was assessed in 398 volunteers who received two doses of the vaccine (n=298) or placebo (n=100). The studied vaccine has shown good tolerability and safety. No deaths, serious adverse events (AE), or other significant AE related to vaccination have been detected. The most common AE in vaccinated participants was pain at the injection site (p<0.05). Immunogenicity assessment was performed in 167 volunteers (122 vaccinated and 45 in Placebo Group) separately for the participants who were anti-SARS-CoV-2 nAB negative (69/122 in Vaccine Group and 28/45 in Placebo Group) or positive (53/122 in Vaccine Group and 17/45 in Placebo Group) at screening. At Day 42 after the first immunization the seroconversion rate in participants who were seronegative at screening was 86.9% with average the geometric mean neutralizing antibody (nAB) titer of 1:20. Statistically significant (p<0.05) increase of IFN-γ production by peptide-stimulated T-cells was observed at Days 14 and 21 after the first immunization. In participants who were seropositive at screening but had nAB titers below 1:256 the rate of 4-fold increase in nAB levels was 85.2%, while in the participants with nAB titers >1:256 the rate of 4-fold increase in nAB levels was below 45%. For the participants who were seropositive at screening the second immunization did not lead to a significant increase in nAB titers. In conclusion, inactivated vaccine CoviVac has shown good tolerability and safety, with 86.9% seroconversion rates in participants, who were seronegative at screening. In participants who were seropositive at screening and had nAB titers below 1:256, a single immunization lead to a 4-fold increase in nAB levels in 85.2% cases. ### Competing Interest Statement A.A.I., A.A.S., V.P.V., M.S.D., L.V.G., N.A.K., R.D.T., G.M.I., A.K.K., E.Y.S., E.O.B., A.S.K., D.V.A., A.N.P., A.A.K., L.P.A., Y.V.R., A.A.S., Y.Y.I., S.E.S., K.A.C, E.G.I., E.A.K., L.I.K. and I.V.G. are employees at the Chumakov Federal Scientific Center for Research and Development of Immune-and-Biological Products of Russian Academy of Sciences, which developed and manufactured CoviVac ### Clinical Trial NCT05046548 ### Funding Statement Study was funded by the Chumakov Federal Scientific Center for Research and Development of Immune-and-Biological Products of Russian Academy of Sciences. ### 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: The study protocol (VKI-I/II-08/20) and its supplementary documentation were approved by the Ethics Committee of the Ministry of Health of the Russian Federation (No. 502 from September 21, 2020). Additionally, the protocol was approved by the local Ethics Committees of the clinical sites, namely Kirov State Medical University of the Ministry of Health of Russia [No. 13/2020 from September 28, 2020]; Healthcare Unit No. 163 of FMBA of Russia, [No.1 from October 11, 2020]; Eco-Safety Scientific Research Center [No. 157 from October 1, 2020]. The study protocol was registered at clinicaltrials.gov (ID [NCT05046548][1]) 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 [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT05046548&atom=%2Fmedrxiv%2Fearly%2F2022%2F02%2F09%2F2022.02.08.22270658.atom