Introduction. Animal models for SARS-CoV-2 infection, reproducing the clinical features of COVID-19 in humans, are important tools for studying the pathogenesis of the disease, transmission of the pathogen and are indispensable for testing antiviral drugs and vaccines. The aim of the study was to assess the virulence and tissue tropism for golden Syrian hamsters of SARS-CoV-2 strains belonging to different epidemiologically significant variants: Wuhan-like, Delta, Omicron BA.1.1 and Omicron BA.5.2. Materials and methods. Hamsters were intranasally infected with different SARS-CoV-2 strains. Virulence and tissue tropism of SARS-CoV-2 strains were assessed by comparing the dynamics of weight, viral load in organs and histopathological changes in lungs in infected and uninfected animals. Results. The Wuhan-like Dubrovka strain had the greatest virulence for hamsters, which was manifested by the development of severe pneumonia and a delay in weight gain by 14.6%, high virus content in the lungs, nasal passages and brain — 6.2, 5,9 and 3.7 lg TCID50/ml of homogenate, respectively. Presumably, it was the infection of the Wuhan-like virus of the central nervous system that negatively affected the weight and general condition of the animals. When hamsters were infected with viruses belonging to the Delta and Omicron variants, the observed minor weight loss in animals was uninformative, so indicators such as lung histopathology, viral load in the lungs, nasal passages, heart and other organs played a decisive role in assessing the virus pathogenicity. A score assessment of lung histopathology was of particular value in assessing the severity of pneumonia, since it reduced subjectivity in evaluating the results of histological examination and provided a semi-quantitative assessment of the pathological process. Conclusion. Despite the revealed lower virulence for hamsters of viruses belonging to the Delta and Omicron variants compared to the ancestral Wuhan virus, this animal model for COVID-19 retains its value for conducting preclinical trials of antiviral drugs.

Introduction. Despite the end of the COVID-19 pandemic, the problem of vaccine prevention of this disease appears highly relevant. The emergence and widespread distribution of the Omicron SARS-CoV-2 variant of concern (VOC) and its sublineages has dramatically reduced the efficacy of vaccination. The possible approach to solving this problem is to develop a nasal live attenuated vaccine capable of activating humoral, mucosal, and cell-mediated immunity, providing a prolonged immune response and cross-protection against different VOCs. The aim of the study was to determine the immunization efficacy with attenuated cold-adapted Wuhan-like SARS-CoV-2 D-D2 strain against homologous and heterologous challenges. Materials and methods. The study was conducted on an animal model of coronavirus pneumonia in golden Syrian hamsters. The efficacy of immunization was assessed by comparing the dynamics of weight, viral load in organs and histopathological changes in the lungs in immunized and unimmunized animals. Results. Single intranasal immunization of golden Syrian hamsters with D-D2 strain showed its high immunogenicity: seroconversion was evident in all immunized animals. Wuhan-like D-D2 strain provides highly effective protection of hamsters against the development of productive infection and pneumonia when challenged both with ancestral virus and heterologous strains related to Delta (AY.122) and Omicron (sublineages BA.1.1 and BA.5.2) variants. Conclusion. SARS-CoV-2 attenuation is a promising strategy for the development of a highly effective nasal live COVID-19 vaccine.

Introduction. The severe consequences of the COVID-19 pandemic highlight the lack of preparedness of national health systems to counter such biological threats. In this regard, the development of preventive means for specific prophylaxis of COVID-19 and other coronavirus diseases remains urgent. The aim of the study was to obtain an attenuated Оmicron-like SARS-CoV-2 strain to create a preventive live attenuated COVID-19 vaccine. Materials and methods. For SARS-CoV-2 infection modeling in vitro and virus propagation, Vero CCL-81 cell culture as well as laboratory strains SARS-CoV-2 Dubrovka (Wuhan-like) and FEB2 (Omicron BA.5.2) were used. Attenuation of the FEB2 strain was carried out by cultivation for 24 passages in Vero CCL-81 cells at a temperature gradually lowered to 24°C, followed by triple cloning. COVID-19 modeling in vivo was performed on golden Syrian hamsters. Viral load was assessed by virus titration by the CPE endpoint and SARS-CoV-2 RNA quantitation in real-time RT-PCR. The primary structure of the SARS-CoV-2 genome was determined by nanopore sequencing. Antibodies to SARS-CoV-2 in hamster sera were detected by ELISA. Results. A non-pathogenic for Syrian hamsters temperature-sensitive (ts) mutant of the omicron-like SARS-CoV-2 F-F3 strain, which possesses attenuation markers such as ts phenotype and reduced immunogenicity, was obtained. The mutant F-F3 strain did not affect the lungs in infected Syrian hamsters, unlike the parental strain, but retained viability in the nasal passages and immunogenicity. A single intranasal immunization of hamsters with the F-F3 ts strain caused seroconversion in them with the production of neutralizing antibodies. An important characteristic of F-F3 strain is low transmissibility and the stability of attenuation phenotype when cultured at 33°C. Conclusions. The combination of the identified characteristics of the attenuated SARS-CoV-2 F-F3 strain indicates the rationality of further investigation of its safety and efficacy in an animal model of COVID-19.

Introduction. Rotavirus infection causes more than 250 million episodes of acute gastroenteritis annually, of which approximately 130,000 cases in children under 5 years of age are fatal. In this regard, the search for drugs for the treatment of rotavirus infection seems extremely relevant.The aim of the research was to evaluate the antiviral activity of Cytovir^®-3 against human rotavirus on a cellular infection model.Material and methods. The objects of the study were a mixture of active ingredients and individual components, identical in composition and ratio, contained in Cytovir^®-3. The study was carried out using a monkey kidney cell culture MA-104 and a laboratory strain of human group A rotavirus — 568, genotype G3P. Cultural, virological, molecular biological and statistical methods were used during the study.Results and discussion. Analysis of the survival of MA-104 cells in the presence of Cytovir^®-3 showed that in the concentration range from 100 to 200 µg/ml, the drug reproducibly exhibited antiviral activity, which was expressed in increased cell survival compared to the viral control. Cytovir^®-3 in a non-toxic concentration of 150 µg/ml suppressed the reproduction of rotavirus by 1.0-2.0 lg СC₅₀/ml with various schemes of introduction into cell culture at all periods of observation, which was accompanied by a significant decrease in the concentration of viral RNA and a cytoprotective effect.

INTRODUCTION. Despite the reclassification of the SARS-CoV-2 coronavirus as an etiological agent of seasonal respiratory viral infections, the problem of developing drugs against COVID-19 remains relevant. The development of antiviral drugs requires an adequate cellular model of infection to search for and test inhibitors of viral reproduction. AIM. To study the feasibility of using a Calu-3 human lung adenocarcinoma cell culture-based test system to evaluate the antiviral activity of recombinant human interferon α-2b (IFNα-2b) against SARS-CoV-2. MATERIALS AND METHODS. SARS-CoV-2 coronavirus, Dubrovka strain (GenBank ID: MW514307.1) was grown in African green monkey kidney (Vero) cell culture. The infectious activity of the virus and the antiviral activity of IFNα-2b were determined in Vero and Calu-3 cell cultures. The antiviral activity of IFNα-2b in Calu-3 cells was assessed by viral antigen accumulation (In-Cell ELISA), and in the Vero cell-based reference test system by cell viability (MTT assay). RESULTS. Optimal conditions for evaluating antiviral activity in Calu-3 cells by measuring viral antigen accumulation in infected cells using In-Cell ELISA have been determined. A study of recombinant IFNα-2b in a Calu-3 cell culture infected with SARS-CoV-2 demonstrated the possibility of highly sensitive determination of antiviral activity indicators such as 50% inhibitory concentration (IC ₅₀ ) and selectivity index. At different infection doses and treatment regimens, the Calu-3-based test system consistently showed greater sensitivity than the reference test system when evaluating IFNα-2b activity. Thus, in Calu-3 cells, the sensitivity of detecting IFNα-2b antiviral activity against SARS-CoV-2, expressed as IC ₅₀ values, was more than 2 log ₁₀ (i.e., 100- to 290-fold) higher than that in Vero cells. The observed differences in the sensitivity of the two test systems may be due to both the different endpoint measurement methods (viral antigen accumulation vs. cell viability) and the deficiency in interferon response genes in Vero cells. CONCLUSIONS. When choosing a test system for evaluating the activity of immunomodulatory drugs (human IFNα-2b, interferon inducers), it is preferable to use Calu-3 cells and determine antiviral activity by viral antigen accumulation. In Vero cells, with assessment of antiviral activity based on cell viability, the therapeutic potential of such drugs may be greatly underestimated.