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Introduction. The study of the mechanisms of transmission of the SARS-CoV-2 virus is the basis for building a strategy for anti-epidemic measures in the context of the COVID-19 pandemic. Understanding in what time frame a patient can spread SARS-CoV-2 is just as important as knowing the transmission mechanisms themselves. This information is necessary to develop effective measures to prevent infection by breaking the chains of transmission of the virus. The aim of the work is to identify the infectious SARS-CoV-2 virus in patient samples in the course of the disease and to determine the duration of virus shedding in patients with varying severity of COVID-19. Materials and methods. In patients included in the study, biomaterial (nasopharyngeal swabs) was subjected to analysis by quantitative RT-PCR and virological determination of infectivity of the virus. Results. We have determined the timeframe of maintaining the infectivity of the virus in patients hospitalized with severe and moderate COVID-19. Based on the results of the study, we made an analysis of the relationship between the amount of detected SARS-CoV-2 RNA and the infectivity of the virus in vitro in patients with COVID-19. The median time of the infectious virus shedding was 8 days. In addition, a comparative analysis of different protocols for the detection of the viral RNA in relation to the identification of the infectious virus was carried out. Conclusion. The obtained data make it possible to assess the dynamics of SARS-CoV-2 detection and viral load in patients with COVID-19 and indicate the significance of these parameters for the subsequent spread of the virus and the organization of preventive measures.

Background: While the world is experiencing another wave of COVID-19 pandemic, global vaccination program is hampered by obvious shortage in supply of licensed vaccines. Development of new vaccines that are easy to manufacture and administer is highly desirable to overcome hurdles in vaccine scaling up and distribution, especially in developing countries. In the effort to satisfy vaccine demands we developed a new single dose vaccine based on recombinant adenovirus type 26 (rAd26) vector carrying the gene for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein – “Sputnik Light”. Methods: We conducted an open label, two-stage, prospective, non-randomized phase I-II trial aimed to assess safety, tolerability and immunogenicity of “Sputnik Light” vaccine in a single center in Russia. Primary outcome measures were antigen-specific humoral immunity (Anti-RBD-SARS-Cov2 antibodies measured by ELISA on days 1, 10, 28, and 42) and safety (number of participants with adverse events monitored throughout the study). Secondary outcome measures were antigen-specific cellular immunity (measured by antigen-dependent CD4+ and CD8+ T-cell proliferation, number of antigen-specific interferon-γ-producing cells as well as interferon-γ concentration upon antigen restimulation) and change in neutralizing antibodies (measured in SARS-CoV-2 neutralization assay). The trial is registered at ClinicalTrials.gov (NCT04713488). Findings: Between January 14 and 27, 2021, 150 participants were screened, of whom 110 were enrolled. Most of solicited adverse reactions were mild (66.4% from all vaccinees), few were moderate (5.5%). No serious adverse events were detected. Assessment of Anti-RBD-SARS-Cov2 antibodies revealed group with pre-existing immunity to SARS-CoV-2. Upon this finding we separated all safety and immunogenicity data according to pre-existing immunity to SARS-Cov2. There were notable differences in the vaccine effects on immunogenicity by the groups. Vaccination of seropositive (N=14) volunteers rapidly boosted RBD-specific IgGs from reciprocal geometric mean titer (​GMT) 594.4 at a baseline up to 26899 comparing to 29.09 in seronegative group (N=96) by day 10. By day 42 seroconversion rate reached 100% (93/93) in seronegative group with GMT 1648. At the same time in seropositive group seroconversion rate by day 42 was 92.9% (13/14) with GMT 19986. Analysis of neutralizing antibodies to SARS-CoV-2 showed 81.7% (76/93) and 92.9% (13/14) seroconversion rates by day 42 with median reciprocal GMT 15.18 and 579.7 in the seronegative and seropositive groups, respectively. Each test to assess cell-mediated immune reactions was carried out on a separate group of 30 volunteers on day 10 upon vaccination. Antigen-specific T cell proliferation, formation of IFNy-producing cells, as well as IFNy secretion were detected in 96.7% (26/27), 96% (24/25) and 96% (24/25) seronegative and in 100% (3/3) 100% (5/5) and 100% (5/5) seropositive vaccinees, correspondingly. Interpretation: The single dose rAd26 vector-based COVID-19 vaccine “Sputnik Light” has a good safety profile and induced strong humoral and cellular immune responses both in seronegative and seropositive participants. Further investigation is needed to assess the effectiveness of this vaccine against COVID-19 used for primary and secondary vaccination. Clinical Trial Registration Details: The trial is registered at ClinicalTrials.gov (NCT04713488). Funding Information: Russian Direct Investment Fund. Declaration of Interests: OVZ, TAO, IVD, OP, DVS, DMG, ASD, AIT, DNS, IBE, EAT, AGB, ASE, FMI, NAN, NLL, ASS, SVB, BSN, DYL, ALG report patents for an immunobiological expression vector, pharmaceutical agent, and its method of use to prevent COVID-19. All other authors declare no competing interests. Ethics Approval Statement: The trial was approved by the local ethic committee and was conducted with the approval of the Ministry of Health of Russian Federation in compliance with International Conference on Harmonization and National Good Clinical Practice guidelines and Declaration of Helsinki.

Summary Background We developed a heterologous COVID-19 vaccine consisting of two components, a recombinant adenovirus type 26 (rAd26) vector and a recombinant adenovirus type 5 (rAd5) vector, both carrying the gene for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein (rAd26-S and rAd5-S). We aimed to assess the safety and immunogenicity of two formulations (frozen and lyophilised) of this vaccine. Methods We did two open, non-randomised phase 1/2 studies at two hospitals in Russia. We enrolled healthy adult volunteers (men and women) aged 18–60 years to both studies. In phase 1 of each study, we administered intramuscularly on day 0 either one dose of rAd26-S or one dose of rAd5-S and assessed the safety of the two components for 28 days. In phase 2 of the study, which began no earlier than 5 days after phase 1 vaccination, we administered intramuscularly a prime-boost vaccination, with rAd26-S given on day 0 and rAd5-S on day 21. Primary outcome measures were antigen-specific humoral immunity (SARS-CoV-2-specific antibodies measured by ELISA on days 0, 14, 21, 28, and 42) and safety (number of participants with adverse events monitored throughout the study). Secondary outcome measures were antigen-specific cellular immunity (T-cell responses and interferon-γ concentration) and change in neutralising antibodies (detected with a SARS-CoV-2 neutralisation assay). These trials are registered with ClinicalTrials.gov, NCT04436471 and NCT04437875. Findings Between June 18 and Aug 3, 2020, we enrolled 76 participants to the two studies (38 in each study). In each study, nine volunteers received rAd26-S in phase 1, nine received rAd5-S in phase 1, and 20 received rAd26-S and rAd5-S in phase 2. Both vaccine formulations were safe and well tolerated. The most common adverse events were pain at injection site (44 [58%]), hyperthermia (38 [50%]), headache (32 [42%]), asthenia (21 [28%]), and muscle and joint pain (18 [24%]). Most adverse events were mild and no serious adverse events were detected. All participants produced antibodies to SARS-CoV-2 glycoprotein. At day 42, receptor binding domain-specific IgG titres were 14 703 with the frozen formulation and 11 143 with the lyophilised formulation, and neutralising antibodies were 49·25 with the frozen formulation and 45·95 with the lyophilised formulation, with a seroconversion rate of 100%. Cell-mediated responses were detected in all participants at day 28, with median cell proliferation of 2·5% CD4+ and 1·3% CD8+ with the frozen formulation, and a median cell proliferation of 1·3% CD4+ and 1·1% CD8+ with the lyophilised formulation. Interpretation The heterologous rAd26 and rAd5 vector-based COVID-19 vaccine has a good safety profile and induced strong humoral and cellular immune responses in participants. Further investigation is needed of the effectiveness of this vaccine for prevention of COVID-19. Funding Ministry of Health of the Russian Federation.