Цель. Оценка проявлений эпидемического процесса COVID-19 среди населения Республики Беларусь в период с февраля 2020 г. по май 2022 г. Материалы и методы. Проведен ретроспективный анализ случаев COVID-19 в Республике Беларусь с начала регистрации (28 февраля 2020 г.) по 8 мая 2022 г. Для оценки динамики выявления новых случаев COVID-19 использовали статистические данные, опубликованные Министерством здравоохранения Республики Беларусь. Результаты. За весь период наблюдения (с 28 февраля 2020 г. по 8 мая 2022 г.) в Республике Беларусь зарегистрировано 982 654 случая заболевания, среднее значение уровня заболеваемости составило 91,4 случая на 100 тыс. населения. Заключение. Развитие эпидемического процесса COVID-19 в Республике Беларусь носило волнообразный характер: в анализируемый период отмечено 4 подъема заболеваемости, отличающихся продолжительностью, показателями, пиковыми уровнями заболеваемости и численностью вовлеченного населения, что обусловлено циркуляцией различных вариантов SARS-CoV-2, изменением иммунной структуры населения, масштабным проведением вакцинации населения, а также реализацией иных санитарно-противоэпидемических мероприятий по предупреждению распространения COVID-19. Purpose. Assessment of the manifestations of the epidemic process of COVID-19 among the population of the Republic of Belarus in the period from February 2020 to May 2022. Materials and methods. A retrospective analysis of COVID-19 cases in the Republic of Belarus was carried out from the beginning of registration (February 28, 2020) to May 8, 2022. To assess the dynamics of identifying new cases of COVID-19, we used statistical data published by the Ministry of Health of the Republic of Belarus. Results. For the entire observation period (from February 28, 2020 to May 8, 2022) 982,654 cases of the disease were registered in the Republic of Belarus, the average incidence rate was 91.4 cases per 100 thousand population. Conclusion. The development of the COVID-19 epidemic process in the Republic of Belarus was characterized by a wave-like nature: during the analyzed period, 4 rises in the incidence rate were noted, differing in duration, indicators, peak incidence levels and the number of the involved population, which is due to the circulation of various variants of SARS-CoV-2, changes in the immune structure of the population, large-scale vaccination of the population, as well as the implementation of other sanitary and anti-epidemic measures to prevent the spread of COVID-19.

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.

Российская Федерация проводит последовательную работу по оказанию содействия странам - партнерам в наращивании научного потенциала и расширении сотрудничества в рамках изучения инфекционных заболеваний. В начале пандемии COVID-19, при поддержке Правительства Российской Федерации Роспотребнадзором была разработана многоэтапная программа серомониторинга иммунитета населения к SARSCoV-2, которая была реализована в Российской Федерации, Кыргызс кой Республике, Республике Беларусь, Республике Армения и Республике Таджикистан. В исследования включили разные возрастные и профессиональных групп перечисленных стран. У волонтеров оценивали уровни IgG антител к двум основным антигенам SARS CoV-2: нуклеокапсиду (Nc) и рецептор-связывающему домену S-белка (RBD) в силу их максимальной представленности во время инфекционного или поствакцинального процессов. В целом, в тех странах, где исследование начали в 2020-2021 году отмечена устойчивая тенденция к росту уровня популяционного иммунитета (доли серопозитивных лиц) в ходе пандемии. А в тех странах которые подключились к исследованию в более поздний период развития пандемии в 2022 году значительная часть населения уже перенесла COVID-19 в манифестной или бессимптомной форме, поэтому не были выявлены статистически значимые возрастные, профессиональные и территориальные отличия в серопревалентности населения как вследствие интенсивного «проэпидемичивания», так и вследствие кампании по вакцинации, начавшейся в середине 2021 года. В первой половине 2021 г. и активно проводившаяся во всех странах вакцинация против коронавируса (как первичная, так и бустерная) стали главными причинами повышения уровня популяционного иммунитета. При этом в структуре серопозитивности произошел сдвиг в сторону увеличения доли лиц, имевших антитела только к RBD. На поздних сроках пандемии в 2022-2023 годах практически у 90% серопозитивных волонтёров гуморальный иммунитет был представлен антителами к обоим антигенам (Nc+RBD). Очевидно, что на поздних сроках пандемии в условиях высокой заболеваемости высоко трансмиссивным штаммом и высокого охвата вакцинацией популяционный иммунитет является «гибридным». The Russian Federation has been working consistently to assist partner countries in building scientific capacity and expanding co-operation in the study of infectious diseases. At the beginning of the COVID-19 pandemic, with the support of the Government of the Russian Federation, Rospotrebnadzor developed a multi-stage programme of seromonitoring of population immunity to SARS-CoV-2, which was implemented in the Russian Federation, the Kyrgyz Republic, the Republic of Belarus, the Republic of Armenia and the Republic of Tajikistan. Different age and professional groups of the countries were included in the studies. IgG antibody levels to two major SARS CoV2 antigens: nucleocapsid (Nc) and receptor-binding domain S-protein (RBD) were assessed in volunteers because of their maximal presence during the infection or postvaccination processes. In general, in those countries where the study began in 2020-2021, there was a steady trend towards increasing levels of population immunity (the proportion of seropositive individuals) during the pandemic. In those countries that joined the study later in the pandemic in 2022, a significant proportion of the population had already experienced COVID-19 in manifest or asymptomatic form, so there were no statistically significant age, occupational or geographic differences in seroprevalence due to both the intensive "pro-epidemic" and the vaccination campaign that began in mid-2021. In the first half of 2021, vaccination against coronavirus (both primary and booster), which was actively carried out in all countries, became the main reasons for the increase in the level of population immunity. At the same time, there was a shift in the structure of seropositivity towards an increase in the proportion of individuals who had antibodies only to RBD. At the late dates of the pandemic in 2022-2023, almost 90% of seropositive volunteers had humoral immunity represented by antibodies to both antigens (Nc+RBD). It is evident that population immunity is "hybrid" in the late pandemic, under conditions of high incidence of a highly transmissible strain and high vaccination coverage. Россия Федерациясы өнөктөш өлкөлөргө илимий потенциалды жогорулатууда жана жугуштуу ооруларды изилдөөдө кызматташтыкты кеңейтүүдө жардам көрсөтүү боюнча ырааттуу иш алып барууда. COVID-19 пандемиясынын башталышында Россия Федерациясынын Өкмөтүнүн колдоосу менен Роспотребнадзор калктын SARS-CoV-2ге каршы иммунитетине серомониторинг жүргүзүү боюнча көп этаптуупрограмманы иштеп чыккан, ал Россия Федерациясында, Кыргыз Республикасында, Беларусь Республикасында, Армения Республикасында жана Тажикстан Республикасында ишке ашырылган. Изилдөөлөр тизмеленген өлкөлөрдүн ар кандай курактагы жана кесипкөй топторун камтыган. Ыктыярчылар SARS CoV-2нин эки негизги антигенине IgG антителолорунун деңгээли боюнча бааланган: нуклеокапсид (Nc) жана S протеининин (RBD) рецепторду байланыштырган домени, алардын инфекциялык же эмдөөдөн кийинки процесстеринде максималдуу өкүлчүлүгүнө байланыштуу. Жалпысынан 2020-2021-жылдары изилдөө башталган өлкөлөрдө пандемия учурунда калктын иммунитетинин деңгээлинин (серопозитивдүү адамдардын үлүшү) жогорулашынын туруктуу тенденциясы байкалган. Ал эми 2022-жылы пандемиянын өнүгүшүнүн кийинки мезгилинде изилдөөгө кошулган өлкөлөрдө калктын олуттуу бөлүгү COVID-19дан манифесттик же симптомсуз түрдө ооруган, ошондуктан статистикалык маанилүү айырмачылыктар жаш курагы, кесиптик жана аймактык калктын, серопреваленттүүлүгү интенсивдүү “эпидемияга каршы” жана 2021-жылдын ортосунда башталган эмдөө өнөктүгүнүн натыйжасында аныкталган жок. 2021-жылдын биринчи жарымында бардык өлкөлөрдө активдүү жүргүзүлүп жаткан коронавируска каршы эмдөө (баштапкы да, бутер да) калктын иммунитетинин деңгээлинин жогорулашынын негизги себептери болуп калды. Ошол эле учурда,серопозитивдүүлүк структурасында RBDга гана антителолору бар адамдардын үлүшүнүн көбөйүшүнө карай жылыш болгон. 2022-2023-жылдардагы пандемиянын кийинки этаптарында серопозитивдүү волонтерлордун дээрлик 90% эки антигендерге (Nc+RBD) антителолор менен гуморалдык иммунитетке ээ болушкан. Пандемиянын кийинки этаптарында, өтө өтүүчү штаммдын пайда болушунун жана вакцинациянын жогорку камтылышынын шарттарында калктын иммунитети “гибриддик” экендиги айдан ачык.

Цель. Изучение эпидемиологических и клинико-лабораторных особенностей и исходов мультисистемного воспалительного синдрома у детей, находившихся на стационарном лечении, на фоне текущей пандемии COVID-19. Материалы и методы. Наблюдалось 63 ребенка с диагнозом «мультисистемный воспалительный синдром (MIS-C), ассоциированный с COVID-19». Диагноз устанавливался согласно критериям CDC/WHO, 2020. Все расчеты проводились в статистическом пакете R, версия 4.1. Результаты анализа считались статистически значимыми при р<0,05. Результаты. Ориентируясь на периоды циркуляции доминирующих коронавирусов, мы сформировали 3 группы пациентов. В 1-ю группу вошли 40 (63,5%) детей, поступивших на лечение с 25.05.2020 по 21.02.2021 («уханьские» штаммы); во 2-ю группу – 9 (14,3%) детей, получивших лечение с 23.02.2021 по 13.06.2021 («альфа»); в 3-ю группу – 14 (22,2%) детей, лечившихся с 01.07.2021 по 19.11.2021 («дельта»). У 47 (74,6%) пациентов наблюдали фенотип MIS-С подобно полной и неполной болезни Кавасаки, неспецифический фенотип в виде наличия признаков шока – у 16 (25,4%) детей. Средний возраст не различался по группам и составил 7±2,5 года, 9,4±4,2 года, 7,9±5 лет соответственно. Все дети имели лихорадку с подъемами температуры до фебрильных цифр 3–4 раза в день и длительностью в среднем 3,2 (1–15) дня. Клинически течение MIS-С у детей не зависело от циркулирующего штамма вируса, дисфункция желудочно-кишечного тракта наблюдалась одинаково часто во всех трех группах (73%, 78% и 57% соответственно). Наблюдалось статистически значимое увеличение количества детей с хейлитом во 2-й (8 детей, 89%) и 3-й (13 детей, 93%) группах, р=0,002. Неврологические нарушения, такие как головная боль, гиперестезии, галлюцинации, светобоязнь, чаще наблюдались у детей в 1-й группе (19 (48%) случаев) и реже во 2-й и 3-й группе (11% и 14% случаев), р=0,022. Патологические регургитации потока крови были наиболее часто встречаемыми нарушениями (68–71%). Из биохимических маркеров воспаления С-реактивный белок (162 мг/л (130; 245), 130 мг/л (90; 160), 130 мг/л (106; 149), р=0,052) регистрировался более высоким у детей в первой группе; прокальцитонин был выше у пациентов третьей группы (4,2 нг/мл (2,4; 8,8), 3,9 нг/мл (3,2; 11,9), 8,7 нг/мл (3,4; 14,1), р=0,625). Заключение. В результате исследования не было обнаружено заметной связи между клиническими или лабораторными особенностями MIS-C и доминирующим циркулирующим штаммом SARS-CoV-2 в заданные периоды времени. При циркуляции штаммов альфа и дельта достоверными отличиями были лишь уменьшение числа пациентов с неврологическими расстройствами и увеличение частоты хейлита, р=0,002. Остальные показатели органной дисфункции были сходными в трех группах детей. В нашем исследовании был 1 (1,6%) летальный исход. Purpose. The study of epidemiological and clinical and laboratory features and outcomes of multisystem inflammatory syndrome in children who were hospitalized against the backdrop of the current COVID-19 pandemic. Materials and methods. In 19 months (May 2020 – December 2021) 63 patients with a diagnosis of "Multisystem inflammatory syndrome in children" (MIS-C) associated with COVID-19 were observed in Anesthesiology and Intensive Care departments of the Healthcare Institution "City Children’s Infectious Clinical Hospital" in Minsk, Republic of Belarus. MIS-C was diagnosed according to CDC/WHO criteria, 2020. All calculations were carried using the R Statistical Package, version 4.1. The results of the analysis were considered statistically significant with p<0.05. Results. Focusing on the periods of circulation of dominant coronaviruses, we generated 3 groups of patients. The 1st group included 40 patients (63.5%) received treatment from 05.25.2020 to 02.21.2021 ("wuhan" strains); the 2nd group comprised 9 children (14.3%) from 02.23.2021 to 06.13.2021 ("alpha"); and the 3rd group consists of 14 children (22.2%) from 07.01.2021 to 11.19.2021 ("delta"). 47 (74.6%) patients had complete and incomplete Kawasaki Disease phenotype of MIS-C; nonspecific phenotype was observed in 16 (25.4%) children. The mean age didn`t differ in study groups. It was 7±2.5; 9.4±4.2; 7.9±5 years respectively. All children presented hyperthermic syndrome with febrile fever 3–4 times a day of an average duration of 3.2 (1–15) days. Clinically, the course of MIS-C in children was not dependent on the circulating strain of the virus, and gastrointestinal dysfunction was observed with equal frequency in all three groups (73%, 78% and 57%, respectively). The only statistically significant increase in number of children with cheilitis was observed in the 2 group – 8 (89%) and the 3 group – 13 (93%), p=0.002. Neurological disorders such as headache, hyperesthesia, hallucinations, photophobia were more frequently observed in the 1st group of children – 19 (48%) cases, and less frequently in the 2nd and 3rd group (in 11% and 14% of cases), p=0.022. Pathological blood flow regurgitation was the most common disorder (68–71%). Several biochemical markers of inflammation levels, such as C-reactive protein (CRP) and procalcitonin (PCT) were high. CRP levels were 162 mg/l (130; 245); 130 mg/l (90; 160); 130 mg/l (106; 149) in 1–2–3 study groups, respectively. In children of the 1st group CRP level was significantly higher, p=0.052. PCT level was higher in patients of the 3rd group (4.2 ng/ml (2.4; 8.8); 3.9 ng/ml (3.2; 11.9); 8.7 ng/ml (3.4; 14.1), respectively, p=0.625). Conclusion. The study revealed no appreciable association between clinical or laboratory features of MIS-C and the dominant circulating strain of SARS-CoV-2 within given time periods. During "alpha" and "delta" strains circulation, only a decrease in the number of patients with neurological disorders and an increase in the frequency of cheilitis were of significant differences, p=0.002. The remaining indicators of organ dysfunction were similar in all three groups of children. There was 1 (1.6%) fatal outcome in our study.

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.

The ongoing coronavirus disease (COVID-19) pandemic over the past three years has caused close attention to the problem of herd immunity, which is understood as: "resistance to the spread of a contagious disease within a population or herd". Collective immunity is formed both as a result of infection (natural spread of the pathogen in a population of susceptible individuals) and as a result of the use of specific vaccines. During the COVID-19 pandemic, both mechanisms for the formation of collective immunity were realized. In the first wave, there was a natural formation of collective immunity to the virus following recoveries from COVID-19 caused by pandemic spread of SARS-CoV-2. Starting from December 2020, the widespread use of specific vaccines against SARS-CoV-2 began in the USA, Great Britain, China, Russia, and a number of other countries. This launched the process of post-vaccination collective immunity formation; its features have depended on the vaccine types implemented. Currently, in those countries where vaccination and revaccination of recovered patients is widely carried out, immunity is "hybrid" in nature. Several commonalities should be noted in the pandemic experience: a somewhat regular, periodic (wavelike) nature of the COVID-19 epidemic process; changes in pathogen genetics in variants in all countries; and expansive mass vaccination programs in many populations. From these, we can draw some conclusions about the general trend for all countries in the formation of collective immunity during the pandemic: At the beginning of the pandemic in 2020, overall population seroprevalence did not exceed 20%. Other findings were: the highest seroprevalence rates were noted in the children's age group; pronounced regional differences were revealed; and the highest indicators were noted among medical workers. Collective immunity developed as a result of infection or illness, and in the majority of seropositive volunteers, it was represented by antibodies to both antigens. At the height of the pandemic in the summer of 2021, population seroprevalence reached 50%. This was due to both a significant number of convalescents and the start of mass vaccination campaigns. In all countries, specific differences in seroprevalence (by age, region, profession) leveled out, leading to more uniformity. During this period, the formation of "hybrid" immunity is clearly prominent, and the proportion of individuals with antibodies to RBD alone increased (due to vaccination with vector vaccines). Later, mass vaccination, as well as involvement of most of the population in the epidemic process due to the emergence of the highly contagious Omicron strain, raised the level of collective immunity to 80-90%. This led to a sharp decrease in COVID-19 incidence in the second half of 2022 in all countries participating in the study. In the later stages of the pandemic (2022-2023), almost 90% of seropositive volunteers had hybrid immunity, reflected as antibodies to both antigens (Nc, RBD).

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.

ResumeIn first two years of COVID-19 pandemic, children usually had a mild or asymptomatic form of the disease. However, in rare cases, after suffering COVID-19, children had clinical manifestations similar to incomplete Kawasaki Disease (CD) or toxic shock syndrome. This condition is known as multisystem inflammatory syndrome in children (MIS-C).The purposeof this research was to study clinical and laboratory features and outcomes of multisystem inflammatory syndrome in children who were hospitalized during COVID-19 pandemic.Materials and methodsIn 19 months (May 2020 – December 2021) 63 patients with a diagnosis of “Multisystem inflammatory syndrome in children” (MIS-C) associated with COVID-19 were observed in the departments of Anesthesiology and Intensive Care of the Healthcare Institution “City Children’s Infectious Clinical Hospital” in Minsk, Republic of Belarus. MIS-C was diagnosed on criteria of CDC/WHO, 2020. All calculations were carried out in the statistical package R, version 4.1. The results of the analysis were considered statistically significant with p<0,05.The results of the studyAll of 63 children with MIS-C didn’t have an acute coronavirus infection. Therefore, it was impossible to determine which strain of SARS-CoV-2 patient exactly had. However, we formed 3 groups of patients based on circulation of the dominant strain of SARS-CoV-2 in Belarus at different times. The 1st group included 40 patients (63,5%) received treatment from 05.25.2020 to 02.21.2021 (“wuhan strains”); the 2nd group – 9 children (14,3%) from 02.23.2021 to 06.13.2021 (“alpha”); the 3rd group – 14 children (22,2%) from 07.01.2021 to 11.19.2021 (“delta”). 47 (74,6%) patients had complete and incomplete Kawasaki Disease phenotype of MIS-C. Nonspecific phenotype was observed in 16 (25,4%) children. It manifested as signs of shock. The mean age didn’t differ in study groups. It was 7±2,5; 9,4±4,2; 7,9±5 years respectively. All children had hyperthermic syndrome. Fever reached febrile numbers 3-4 times a day. Average fever duration was 3,2 [1–15] days. The course of MIS-C in children also didn’t depend on the circulating strain of the virus. For instance, gastrointestinal dysfunction was observed in all three groups with equal frequency (73%, 78% and 57%, respectively). The only a statistically significant increase was in the number of children with cheilitis. In the 2nd group 8 children (89%) and the 3rd group 13 children (93%) had cheilitis, respectively, p=0,002. Neurological disorders such as headache, hyperesthesia, hallucinations, photophobia were more often observed in the 1st group of children - 19 (48%) cases and less frequently in the 2nd and 3rd group (in 11% and 14% of cases), p=0,022. Pathological blood flow regurgitation was the most common disorder (68-71%). Several biochemical markers of inflammation levels, such as C-reactive protein (CRP) and procalcitonin (PCT), were high. CRP levels were 162 mg/l [130; 245]; 130 mg/l [90; 160]; 130 mg/l [106; 149] in 3 study groups, respectively. In children of the 1st group CRP level was significantly higher, p=0.052. PCT level was higher in patients of the 3rd group (4.2 ng/ml [2,4; 8,8]; 3.9 ng/ml [3,2; 11,9]; 8.7 ng/ml [3,4; 14,1], p=0.625).ConclusionAs a result of the research there wasn’t found notable connection between clinical or laboratory features of MIS-C and the dominant circulating strain of SARS-CoV-2 in given time periods. During the circulation of “alpha” and “delta” strains, the only significant differences were decrease of the number of patients with neurological disorders and increase in the frequency of cheilitis, p=0,002. The remaining indicators of organ dysfunction were similar in three groups of children. There was 1 (1,6%) fatal outcome in our study.

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.