N-protein vaccine Convacell® is effective against COVID-19: phase 3, randomized, double-blind, placebo-controlled clinical trial

We have developed a Convacell®, a COVID-19 vaccine based on the conservative viral nucleocapsid (N) protein. The N protein is evolutionary conservative and is abundantly expressed on the surface of infected cells, allowing anti-N immune response generated by Convacell® to rapidly clear infected cells and provide long-lasting protection against COVID-19. Convacell® has been demonstrated to be safe and highly immunogenic, creating immune responses lasting over a year, in phase I/II and IIb clinical trials. Phase IIb clinical trial has also demonstrated that a single dose vaccination regimen with Convacell® is sufficient to provide an immune response. Here we report the finding of the phase III clinical trial of Convacell®. Two groups of volunteers from Russia have been either vaccinated with a single dose of Convacell® or injected with placebo, and then monitored for incidence of COVID-19 and adverse effects. Anti-N antibody titers at admission were also analyzed, to take into account for potential effects of previous virus encounters. Disease incidence over 6 months results indicate an overall vaccine efficacy of 85.2% (95% confidence interval: 67.4-93.3%). Additionally, Convacell® has shown a good safety profile. Overall, Convacell® demonstrated highly desirable qualities and good performance as a vaccine and can be considered as valuable COVID-19 preventative measure. ### Competing Interest Statement Sevastyan Rabdano, Iuliia Pletyukhina, Nikita Saveliev, Fakhretdinova Liliya, Ekimov Aleksey, Veronika Skvortsova, and Sergei Arakelov report patents for genetic constructs and vaccine composition. The other authors have no conflicts of interest to declare. ### Clinical Trial NCT05726084 ### Funding Statement This study was funded by Saint Petersburg Scientific Research Institute of Vaccines and Serums of the Federal Medical-Biological Agency of Russia. ### 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: Ethics Committee of the Ministry of Health of the Russian Federation gave ethical approval for this work (decision #583 from 5 October 2022). 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, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.