Background. The course of the COVID-19 epidemic process depends on population immunity which prevents pathogen spread. Aim: to study an evolution of SARS-CoV-2 humoral immunity in the Belarusian population rela- tive to COVID-19 pandemic dynamics. Materials and methods. The work was carried out according to a methodology for assessing herd immunity developed by Rospotrebnadzor (Russia) and the Belarusian Ministry of Health involving the St. Petersburg Pasteur Institute (SPPI) by taking into account the WHO recommendations. The study was approved by the Bioethics Committee of Belarus and the SPPI Bioethics Committee. Participant selection was carried out by ques- tionnaire using a cloud (internet server) service. To monitor herd immunity, a cohort of 4661 subjects (involved at all stages of seromonitoring) was formed from the total volunteer group. Study subjects were randomized into groups based on age (117, 1829, 3039, 4049, 5059, 6069, 70+ years), geographic region, and occupation. For the detection of antibodies (Abs) against SARS-CoV-2 nucleocapsid (Nc) and S glycoprotein receptor-binding domain (RBD), rel- evant assay systems were used according to the manufacturers instructions. A four-stage study was conducted according to a unified scheme. Results. At stage 1 (pandemic month 15), herd immunity was mainly accounted for by Nc+RBD+ Ab status alone. By stage 2 (4 months later), its specific proportion decreased by 1.2-fold, whereas percentage of subjects solely bearing RBD-specific Abs increased by 1.7-fold. At stages 3 and 4 (9 and 19 months after the onset) vs. stage 2, percent- age of subjects with RBD+Nc decreased by 3.5%; the proportion of persons with Nc+RBD Abs increased by 1.5-fold. The most important contributor in herd immunity turned out to be due to population vaccination, with coverage reaching 70% by stage 4. Among vaccines, compared with whole-virion, inactivated BIBP-CorV vaccine the Sputnik V and Sputnik Light vector were used most often. Conclusion. The evolution of herd SARS-CoV-2 humoral immunity included a series of changes in circulating Ab levels (Nc, RBD). The hybrid immunity formed helped to reduce the incidence of COVID-19 to sporadic level.

Цель. Оценка уровня популяционного иммунитета к SARS-CоV-2 среди населения Гродненской области Республики Беларусь на втором году пандемии COVID-19. Материалы и методы. Оценка популяционного иммунитета к SARS-CоV-2 среди населения Гродненской области проведена в рамках трехэтапного продольного стратифицированного по возрасту сероэпидемиологическогоисследования, включавшего анкетирование и изучение серопревалентностик RBD-фрагменту S-белка SARS-CoV-2. Определение суммарных (IgM и IgG) антител к SARS-CoV-2 осуществляли с помощью качественной иммуноферментной тест-системы Wantai SARS-CoV-2 Total Ab (Beijing Wantai Biological Pharmacy Enterprise, Пекин, Китай). Результаты. Спустя год с момента регистрации первого случая COVID-19 коллективный иммунитет населения Гродненской области составил 58,8%. Доля серопозитивных участников увеличилась на последующих этапах. На первом и третьем этапах статистически значимых различий в уровне серопревалентности как среди детского и взрослого населения, так и среди различных возрастных групп населения не выявлено. На втором этапе исследования наименьшая доля серопозитивных лиц была в возрастной группе 60–69 лет, а наибольшая – в возрастной группе 30–39 лет. Не установлено статистически значимых различий в уровне серопревалентности среди профессиональных групп, а также среди лиц с различным социальным поведением. Заключение. С учетом развития эпидемиологической ситуации, появления новых вариантов вируса SARS-CоV-2, а также продолжающейся вакцинации населения целесообразно дальнейшее изучение динамики формирования популяционного иммунитета. Purpose. Evaluation of the level of population immunity to SARS-CoV-2 among the population of the Grodno region of the Republic of Belarus in the second year of the COVID-19 pandemic. Materials and methods. Evaluation of population immunity to SARS-CoV-2 among the population of the Grodno region was carried out within the framework of a 3-stage longitudinal stratified by age seroepidemiological study, which included questionnaires and a study of the seroprevalence to the RBD fragment of the SARS-CoV-2 S protein among the population. Determination of total (IgM and IgG) antibodies to SARS-CoV-2 was carried out using the qualitative enzyme immunoassay kit Wantai SARS-CoV-2 Total Ab (Beijing Wantai Biological Pharmacy Enterprise, Beijing, China). Results. A year after the registration of the first case of COVID-19, the population immunity of the population of the Grodno region was 58.8%. The proportion of seropositive participants increased in subsequent stages. At the first and third stages, there were no statistically significant differences in the level of seroprevalence both among the child and adult population, and among different age groups of the population. In the second phase of the study, the smallest proportion of seropositive individuals was in the 60–69 age group, and the highest in the 30–39 age group. There were no statistically significant differences in the level of seroprevalence among occupational groups, as well as among persons with different social behaviors. Conclusion. Taking into account the development of the epidemiological situation, the emergence of new variants of the SARS-CoV-2 coronavirus, as well as the ongoing vaccination of the population, it is advisable to further study the dynamics of the formation of population immunity.

Цель. Оценка уровня популяционного иммунитета к SARS-CоV-2 среди населения Гомельской области Республики Беларусь на втором году пандемии COVID-19.Материалы и методы. Оценка популяционного иммунитета к SARS-CоV-2 среди населения Гомельской области проведена в рамках 3-этапного продольного стратифицированного по возрасту сероэпидемиологического исследования, включавшего анкетирование и изучение серопревалентности к RBD фрагменту S белка SARS-CoV-2. Определение суммарных (IgM и IgG) антител к SARS-CoV-2 осуществляли с помощью качественной иммуноферментной тест-системы Wantai SARS-CoV-2 Total Ab (Beijing Wantai Biological Pharmacy Enterprise, Пекин, Китай).Результаты. Уже на первом этапе исследования уровень серопревалентности населения Гомельской области Республики Беларусь к RBD фрагменту S белка SARS-CoV-2 составил 66,4%. Доля серопозитивных участников увеличилась на последующих этапах. Если на первом этапе статистически значимых различий в уровне серопревалентности как среди детского и взрослого населения, так и среди различных возрастных групп населения не выявлено, то на втором и третьем этапах исследования уровень серопревалентности среди взрослого населения был достоверно выше, чем среди детского. Также выявлены значимые различия в уровне серопревалентности среди различных возрастных групп детского и взрослого населения. Определенным фактором риска в распространении коронавирусной инфекции является принадлежность к профессиональным группам. При оценке влияния на уровень серопревалентности факторов риска, связанных с образом жизни, а также с использованием общественного транспорта, статистически значимых различий не выявлено.Заключение. С учетом развития эпидемиологической ситуации, появления новых вариантов вируса SARS-CоV-2, а также продолжающейся вакцинации населения целесообразно дальнейшее изучение динамики формирования популяционного иммунитета. Purpose. Evaluation of the level of population immunity to SARS-CoV-2 among the population of the Gomel region of the Republic of Belarus in the second year of the COVID-19 pandemic.Materials and methods. Evaluation of population immunity to SARS-CoV-2 among the population of the Gomel region was carried out within the framework of a 3-stage longitudinal stratified by age seroepidemiological study, which included questionnaires and a study of the seroprevalence to the RBD fragment of the SARS-CoV-2 S protein among the population. Determination of total (IgM and IgG) antibodies to SARS-CoV-2 was carried out using the qualitative enzyme immunoassay kit Wantai SARS-CoV-2 Total Ab (Beijing Wantai Biological Pharmacy Enterprise, Beijing, China).Results. Already at the first stage of the study, the level of seroprevalence of the population of the Gomel region of the Republic of Belarus to the RBD fragment of the SARS-CoV-2 S protein was 66.4%. The proportion of seropositive participants increased in subsequent stages. If at the first stage there were no statistically significant differences in the level of seroprevalence both among the child and adult population, and among different age groups of the population, then at the second and third stages of the study, the level of seroprevalence among the adult population was significantly higher than among the children’s. Significant differences in the level of seroprevalence among different age groups of children and adults were also revealed. A certain risk factor in the spread of coronavirus infection is belonging to professional groups. When assessing the effect on the level of seroprevalence of risk factors associated with lifestyle, as well as with the use of public transport, no statistically significant differences were revealed.Conclusion. Taking into account the development of the epidemiological situation, the emergence of new variants of the SARS-CoV-2 coronavirus, as well as the ongoing vaccination of the population, it is advisable to further study the dynamics of the formation of population immunity.

Abstract: This is an analysis of the features of the COVID-19 pandemic the population of the Republic of Belarus from February 2020 to January 2021, the characteristics of sanitary and anti-epidemic measures carried out in the country, assessment of study the safety (tolerance) of the vaccines used the epidemiological efficacy of the vaccination. A retrospective analysis of COVID-19 cases in the Republic of Belarus from the beginning of registration (February 28, 2020) to January, 3, 2022 was performed. Vaccine safety (tolerance) and efficacy were assessed in an observational study. Safety (tolerance) was assessed by presence/absence of adverse reactions: general (fever, malaise, headache, muscle pain, runny nose, nausea, vomiting, sore throat, etc) and local ones (redness, swelling, soreness at the injection place). The COVID-19 pandemic in the Republic of Belarus is characterized by successive development stages: from no cases in early 2020 to detected cases where most individuals had no history of contact with COVID-19 patients; periods of rising and falling incidence Vaccines against COVID-19 (Gam-COVID-Vac (Russia), inactivated vaccine against SARS-CoV-2 (Vero Cell) Sinopharm / BIBP (China) demonstrated a high safety profile in mass vaccination of the population of the Republic of Belarus.

Objective was to investigate the SARS-CoV-2 collective immunity status of the population of Belarus within the context of the COVID-19 pandemic. Materials and methods. The work was carried out according to the methodology for assessing SARS-CoV-2 population immunity, developed by Rospotrebnadzor Russia and the Ministry of Health of Belarus with the participation of the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The Bioethics Committee of Belarus and the local ethics committee of the St. Petersburg Pasteur Institute approved the study. Selection of participants was carried out using a questionnaire method and online technology (internet, cloud server). Volunteers were randomized into seven age groups (years of age): 1–17; 18–29; 30–39; 40–49; 50–59; 60–69; and 70+. Regional randomization ensured proportional representation of volunteers from each region, and no more than 30 people were included from one enterprise. In accordance with manufacturer instructions, blood plasma samples were analyzed for: IgG antibodies (Abs) to the SARS-CoV-2 nucleocapsid (Nc) using a quantitative ELISA test system; and IgG Abs to the receptor binding domain (RBD) of the SARS-CoV-2 S (spike) surface glycoprotein using a qualitative ELISA test system. Statistical processing was carried out using Excel 2010 and other software. Statistical differences were designated as significant when p 0.05, unless otherwise indicated. Results. The level of seroprevalence, in terms of Abs to Nc among the Belarusian population, was 38.4% (95% CI 37.6–45.4). The highest Ab levels were found among individuals in older age groups (50-70+ years old). The lowest were found in children 1–17 years old and in young people 18–39 years old The distribution of seroprevalence across Belarusian regions was relatively homogeneous, with the exception of the Minsk Region, where a statistically significant decrease in the indicator was noted. In terms of profession, the largest share of seropositive individuals was found among transportation workers; the smallest was found in business. The moderate COVID-19 incidence has not led to a dramatic increase in the number of contacts. The base reproduction number (R0) was 1.3. In the Republic of Belarus, there was a moderate level of asymptomatic COVID-19 among seropositive individuals (45.3% [95% CI 44.0–46.7]). This form of infection was observed most often among children aged 1–17 years old (65.0% [95% CI 61.3–68.6]). In parallel with seroprevalence assessment, SARS-CoV-2 vaccination was carried out. We used two vaccines: Gam-COVID-Vac (also known as Sputnik V, developed by Gamaleya National Center for Epidemiology and Microbiology, Russia); and BBIBP-CorV (Sinopharm, PRC). Vaccination against SARS-CoV-2 was accompanied by an increase in the level of anti-RBD Abs (95% [95% CI 94.7–96.7]). Taking into account the vaccination of a subset of the population with BBIBP-CorV, the overall herd immunity, inferred from the analyzed indicators (presence of anti-Nc or anti-RBD Abs), was 47.1% (95% CI 46.3–48.0). Conclusion. COVID-19 in Belarus was characterized by a moderately pronounced course of the epidemic process. The threshold level of herd immunity to SARS-CoV-2 has not yet been reached, as a result of which the conditions for progression of the epidemic remain.

Objective. To study the COVID-19 pandemic features among the population of the Republic of Belarus from February 2020 to September 2021 and assess the safety (tolerance) and epidemiological efficacy of the Gam-COVID-Vac vaccine (Sputnik V). Materials and methods. A retrospective analysis of COVID-19 cases in the Republic of Belarus from the beginning of registration (February 28, 2020) to September 12, 2021 was performed. To assess the COVID-19 case detection dynamics, official registration data available on the website of the Ministry of Health of the Republic of Belarus were used. Vaccine safety (tolerance) and efficacy were assessed in an observational study. Safety (tolerance) was assessed by presence/absence of adverse reactions: general and local ones. The efficacy rate (E) and the epidemiological efficacy index (K) was calculated according to the formula: E(%)=100*(b-a)/b, K=b/a. Results. Our data show that The COVID-19 pandemic in the Republic of Belarus is characterized by successive development stages: the first is the absence of COVID-19 cases in the country; the second is the registration of individual infection cases that came from abroad followed by local pathogen spread among the country's population; the third is a local spread of COVID-19 among individuals who had contact with infected people; the fourth is the detection of cases where patients had no history of exposure to COVID-19 patients. As of calendar week 26, 2021 Delta variant of SARS-CoV-2 has become the prevalent in the country. Follow-up results in January-August 2021 showed that the Sputnik V vaccine was well tolerated, with 80,832 adverse reactions reported (2.99% (95% CI 2.9-3.0) of the total number of vaccine doses administered). In terms of severity, adverse reactions were mild (91.4% (95% CI 91.2-91.6)) and moderate (8.6% (95% CI 8.6-8.8)). The epidemiological efficacy rate was 96.3%, the epidemiological efficacy index was 26.7. Thus, the results obtained testify to high prophylactic efficacy of the Sputnik V vaccine. Conclusions. The COVID-19 pandemic in the Republic of Belarus is characterized by successive development stages: from no cases in early 2020 to detected cases where most individuals had no history of contact with COVID-19 patients; periods of rising and falling incidence. The Sputnik V vaccine has demonstrated a high safety profile and epidemiological efficacy throughout mass vaccination in the Republic of Belarus.