Characteristics of the Herd Immunity to SARS-CoV-2 in Residents of the Saratov Region under COVID-19 Epidemic

The global community is experiencing one of the largest infectious disease outbreaks in the 21st century. In the Saratov Region, the first case of new coronavirus infection was confirmed on March 19, 2020.The maximum increase in cases was noted between May 15 and June 30, during that time the total number of infected people in the region increased from 1526 to 6444. Since July 2020, a stable incidence level of new coronavirus infection has been observed in the Saratov Region, without a steady decline.The aim of the study was to assess the status of population immunity to the SARS-CoV-2 virus among residents of Saratov and the Saratov Region under the COVID-19 epidemic.Materials and methods. In the period from June 23 to July 26, 2020, a serological study of blood samples from 3372 volunteers of different age groups was conducted. The content of antibodies to SARS-CoV-2 was determined by ELISA using a set of reagents “ELISA anti-SARS-CoV-2 IgG” produced by the State Scientific Center of Applied Microbiology and Biotechnology of the Rospotrebnadzor (Russia).Results and discussion. In general, the incidence of COVID-19 in the Saratov Region is taking place against the background of moderate seroprevalence to the SARS-CoV-2 virus, accompanied by a high incidence of non-apparent (asymptomatic) forms of the infectious process. The absence of clinical symptoms of the disease, in the context of the limited use of methods for determining the RNA of the SARS-CoV-2 virus in PCR (11 % of the region’s population) makes it difficult to assess the real spread of the virus in the population and to establish the timing of the formation of persistent herd immunity. A low rate of antibody response among individuals with a positive result of PCR analysis, as well as among volunteers who had an infection in May, June 2020, indicates a weak formation of the immune response, or the prevalence of individuals reacting mainly by activating the cellular link of the immune system in the population. The obtained results, although they need to be explained in a number of respects, can be applied to the organization of preventive measures, including vaccination, in the region.

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Herd Immunity to SARS-CoV-2 among the Population in Saint-Petersburg during the COVID-19 Epidemic

Problems of Particularly Dangerous Infections ◽

10.21055/0370-1069-2020-3-124-130 ◽

2020 ◽

pp. 124-130 ◽

Cited By ~ 1

Author(s):

A. Yu. Popova ◽

E. B. Ezhlova ◽

A. A. Mel’nikova ◽

N. S. Bashketova ◽

R. K. Fridman ◽

...

Keyword(s):

Herd Immunity ◽

Age Groups ◽

Active Phase ◽

Asymptomatic Infection ◽

Exclusion Criterion ◽

Pcr Analysis ◽

First Case ◽

History Of ◽

The Unemployed ◽

Selection Of

The first case of COVID-19 was diagnosed in St. Petersburg on March 2, 2020; the period of increase in the incidence lasted for 10 weeks, the maximum rates were recorded in mid-May, and subsequently there was a statistically significant decrease in the incidence.Objective: to determine the level and structure of community immunity to SARS-CoV-2 among the population of St. Petersburg during the period of intensive spread of COVID-19.Materials and methods. Selection of volunteers for the study was carried out through interviewing and randomization. The exclusion criterion was active COVID-19 infection at the time of the survey. 2713 people aged 1 to 70 years and above were examined for the presence of specific antibodies to SARS-CoV-2. Antibodies were detected by enzyme immunoassay.Results and discussion. Studies have shown that in St. Petersburg, in the active phase of COVID-19 epidemic, there was a moderate seroprevalence to SARS-CoV-2, which amounted to 26 %, against the background of a high frequency (84.5 %) of asymptomatic infection in seropositive individuals who did not have a history of COVID-19 disease, positive PCR result and ARI symptoms on the day of examination. The maximum indicators of herd immunity were established in children 1–6 years old (31.1 %), 7–13 years old (37.7 %) and people over 70 years old (30.4 %). Differences in the level of seroprevalence in the age groups of 18–49 years are statistically significant. The highest level of seroprevalence was found among the unemployed (29.7 %), healthcare workers (27.1 %), education sector (26.4 %) and business sector personnel (25 %). In convalescents, COVID-19 antibodies are produced in 75 % of cases. In individuals with positive result of PCR analysis carried out earlier, antibodies are detected in 70 % of the cases. The results of the study of herd immunity to SARS-CoV-2 are essential to forecast the development of the epidemiological situation, as well as to plan measures for specific and non-specific prevention of COVID-19.

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Collective immunity to SARS-CoV-2 of Moscow residents during the COVID-19 epidemic period

Infekcionnye bolezni ◽

10.20953/1729-9225-2020-4-8-16 ◽

2020 ◽

Vol 18 (4) ◽

pp. 8-16

Author(s):

A.Yu. Popova ◽

◽

E.B. Yezhlova ◽

A.A. Melnikova ◽

E.E. Andreeva ◽

...

Keyword(s):

Herd Immunity ◽

Age Groups ◽

Asymptomatic Infection ◽

Administrative District ◽

Cultural Workers ◽

Population Immunity ◽

The North ◽

First Case ◽

Epidemic Period ◽

Structure Of Population

The coronavirus disease pandemic (COVID-19) was announced by WHO in February 2020. In Moscow, the first case of the disease was detected on March 2, 2020 in a man who arrived from Italy. Two weeks after the first case, there was an exponential increase in the number of cases. The incidence peaked in the 19th week of the year, followed by a steady decline, lasting 16 weeks. Objective. To investigate the level and structure of population immunity to the SARS-CoV-2 virus among the population of Moscow against the background of the incidence of COVID-19. Patients and methods. The study of population immunity of Moscow residents to SARS-CoV-2 was carried out in the period from July 1, 2020 to July 30, 2020 against the background of stabilization of the incidence rate. The work was conducted as part of the first stage of the Rospotrebnadzor project to assess population immunity to the SARS-CoV-2 virus among the population of the Russian Federation, taking into account the protocol recommended by WHO. Volunteers for the study were selected by the method of questioning and randomization. The results of the survey of 2688 people were included in the analysis. The number of volunteers in all age groups was 384–385 people. The content of specific IgG to the SARS-CoV-2 nucleocapsid was determined by the enzyme-linked immunosorbent assya using a kit produced by FBIS SRCAMB according to the manufacturer's instructions. Results. During the survey of volunteers it was found that the share of seroprevalent residents of Moscow was 22.1%. By age groups, the highest proportion of seroprevalent was found among children aged 14–17 years (44.6%), the lowest (15.9%) – among people aged 18–29 years. Seroprevalence had no gender differences. The lowest level of herd immunity was revealed in the North-Western Administrative District (16.8%), the highest – in the South-Eastern Administrative District, as well as in the Troitsky and Novomoskovsky Administrative Districts of Moscow (in both, 24.1%). The smallest number of seropositive persons was among cultural workers (5.8%), the largest – among medical workers (27.0%). In the presence of contacts with patients with COVID-19, the probability of seroconversion increases by 1.5 times, and among convalescing persons COVID-19 antibodies were detected in 60.0% of cases. The proportion of people with asymptomatic infection among seropositive residents was 82.4%. Conclusion. The results obtained make it possible to characterize the population immunity of Moscow residents and are essential for the planning and implementation of anti-epidemic measures during the incidence of COVID-19. Key words: coronaviruses, SARS-CoV-2, seroprevalence, population, COVID-19

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The second wave: estimating the hidden asymptomatic prevalence of COVID-19 in Ireland as we plan for imminent immunisation

HRB Open Research ◽

10.12688/hrbopenres.13206.1 ◽

2021 ◽

Vol 4 ◽

pp. 19

Author(s):

Catherine Comiskey ◽

Anne Snel ◽

Prakashini Banka

Keyword(s):

Clinical Symptoms ◽

Descriptive Analysis ◽

Age Groups ◽

Mitigation Measures ◽

Current Evidence ◽

First Case ◽

Total Prevalence ◽

Time Period ◽

Back Calculation ◽

Asymptomatic Individuals

Since the first case of COVID-19 in Ireland was recorded policy makers have introduced mitigation measures to control the spread of infection. Infection is spread by both known cases and hidden, undetected asymptomatic cases. Asymptomatic individuals are people who transmit the virus but display no clinical symptoms. Current evidence reveals that this population is a major contributing factor to the spread of the disease. There is little or no knowledge of the scale of the hidden prevalence of all infections both asymptomatic and symptomatic in Ireland. Furthermore, as governments plan for the roll out of imminent immunisation programmes, the need to know the scale of the hidden prevalence and hence knowledge of the level of immunisation required is essential. We describe and analyse the numbers of reported cases of COVID-19 in Ireland from the first case in February 2020 to mid-December 2020. Using the method of back-calculation we provide estimates of the asymptomatic prevalence of cases from June to December 2020. The descriptive analysis highlighted two epidemic waves of known cases in the time period. Wave two from June to December included twice as many cases as wave one and cases were significantly younger. The back-calculation estimates of asymptomatic prevalence during this time period revealed that for every case known there was an additional unknown case and total prevalence in wave two was estimated to be approximately 95,000 as opposed to the reported 48,390 cases. As prevalence in wave two is known to be spreading within and from younger age groups the role of mixing patterns on spread needs to be disseminated to the wider public to adequately inform them how personal modifications in behaviour can contribute to the control of the epidemic. While universally imposed lockdowns and mitigation measures may be essential, personal behavioural mixing choices are powerful protectors.

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The structure of seroprevalence to the SARS-CoV-2 virus among residents of the Moscow Region during the period of epidemic incidence of COVID-19

Infekcionnye bolezni ◽

10.20953/1729-9225-2020-4-17-26 ◽

2020 ◽

Vol 18 (4) ◽

pp. 17-26

Author(s):

A.Yu. Popova ◽

◽

E.B. Ezhlova ◽

A.A. Melnikova ◽

O.M. Mikailova ◽

...

Keyword(s):

Large Scale ◽

Medical Center ◽

Age Groups ◽

Maximum Level ◽

Test System ◽

Moscow Region ◽

Pcr Analysis ◽

Enzyme Linked Immunosorbent Assay ◽

Population Immunity ◽

First Case

A pandemic of the disease caused by the SARS-CoV-2 virus (hereinafter referred to as COVID-19) was announced by WHO in February 2020. In the Moscow Region (MR), the first case of the disease was detected on March 7, 2020 in a woman who arrived from Switzerland. Four weeks later, a rapid rise began, the peak of which fell on the 20th week (May 11, 2020 – May 17, 2020), which was replaced by a gradual steady decline that lasted for 13 weeks. Objective. To determine the level and structure of population immunity to the SARS-CoV-2 virus among the population of the Moscow Region between June 22, 2020 and July 11, 2020. Patients and methods. A serological study of seroprevalence among residents of MR to COVID-19 was carried out from June 22, 2020 till July 11, 2020 during the period of a steady decline in the incidence. The work was conducted as part of the first stage of the large-scale Rospotrebnadzor program to assess population immunity to the COVID-19 virus among the population of the Russian Federation. Volunteers for the study were selected by the method of questioning and randomization. The analysis included the results of a survey of 2688 people. The number of volunteers in all age groups was equal. The content of specific IgG to the COVID-19 nucleocapsid was determined by the enzyme-linked immunosorbent assay using a test system manufactured by the FBIS SRCAMB according to the manufacturer's instructions. Results. The results of the study showed that the collective immunity of the total population of the Moscow Region was 21.0%. The maximum level of population immunity was established in children aged 14–17 years (30.7%) and 1–6 years old (25.2%). There were no statistically significant differences in the level of seroprevalence between men and women. As a result of seroepidemiological research, it was shown that in the medical center, in the presence of contacts with patients with COVID-19, the risk of infection increases by 2.5 times. After infection with COVID-19, antibodies were detected in 78.7% of cases. In persons with a positive result of the PCR analysis obtained earlier, antibodies were detected in 82.8% of cases. A high proportion of asymptomatic infection among seropositive volunteers was found, which amounted to 83.4%. Key words: coronaviruses, SARS-CoV-2, incidence, seroprevalence, the Moscow Region, population, COVID-19

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Coronavirus disease in children in the Omsk region

CHILDREN INFECTIONS ◽

10.22627/2072-8107-2020-19-4-30-33 ◽

2020 ◽

Vol 19 (4) ◽

pp. 30-33

Author(s):

Yu. B. Belan ◽

E. A. Gashina ◽

E. Lobova ◽

L. A. Bezrukova

Keyword(s):

Clinical Symptoms ◽

Outpatient Basis ◽

Upper Respiratory Tract ◽

Mild Form ◽

Infected People ◽

Epidemiological Features ◽

Coronavirus Infection ◽

Upper Respiratory ◽

Tract Damage ◽

The City

The study of the infection caused by the SARS-CoV-2 coronavirus is highly relevant. Objective: To study the clinical and epidemiological features of a new coronavirus infection in children in the city of Omsk and the Omsk region during the 2020 epidemic. Materials and methods. We conducted a retrospective study of 68 children aged 1—18 years diagnosed with new coronavirus disease and receiving medical treatment in Infectious Diseases Hospital of City Children's Clinical Hospital № in Omsk between April and September 2020. In all children, the diagnosis was confirmed by examination of nasopharyngeal / oropharyngeal swabs for RNA SARS-CoV-2 by PCR. Results. Among those hospitalized prevailed children over 10 years old (61.7%), no reliable difference based on sex was observed. 83.8% of children contacted with COVID-19-infected people. Most children had the new coronavirus infection in mild form (61.8%) with upper respiratory tract damage. Pneumonia was recorded only in 16.2% of examined children over the age of 10. The key clinical symptoms in childhood were: yawn hyperemia, fever and cough. Impaired sense of smell in the form of hyposmia and anosmia developed only in children over the age of 10. Leukopenia detection in blood in moderate forms correlated with the presence of pneumonia. Conclusion. Given the mild course of COVID-19 in children, early isolation and treatment on an outpatient basis should be considered the most effective approach to patient management.

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SARS-CoV-2 Seroprevalence Structure of the Russian Population during the COVID-19 Pandemic

Viruses ◽

10.3390/v13081648 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1648 ◽

Cited By ~ 1

Author(s):

Anna Y. Popova ◽

Viacheslav S. Smirnov ◽

Elena E. Andreeva ◽

Elena A. Babura ◽

Sergey V. Balakhonov ◽

...

Keyword(s):

Herd Immunity ◽

Population Sample ◽

Age Groups ◽

Phase Curve ◽

Initial Increase ◽

Two Phase ◽

Scientific Center ◽

Continuous Increase ◽

Rate Of Increase ◽

Federal Districts

The SARS-CoV-2 pandemic, which came to Russia in March 2020, is accompanied by morbidity level changes and can be tracked using serological monitoring of a representative population sample from Federal Districts (FDs) and individual regions. In a longitudinal cohort study conducted in 26 model regions of Russia, distributed across all FDs, we investigated the distribution and cumulative proportions of individuals with antibodies (Abs) to the SARS-CoV-2 nucleocapsid antigen (Ag), in the period from June to December 2020, using a three-phase monitoring process. In addition, during the formation of the cohort of volunteers, the number of seropositive convalescents, persons who had contact with patients or COVID-19 convalescents, and the prevalence of asymptomatic forms of infection among seropositive volunteers were determined. According to a uniform methodology, 3 mL of blood was taken from the examined individuals, and plasma was separated, from which the presence of Abs to nucleocapsid Ag was determined on a Thermo Scientific Multiascan FC device using the “ELISA anti-SARS-CoV-2 IgG” reagent set (prod. Scientific Center for Applied Microbiology and Biotechnology), in accordance with the developer’s instructions. Volunteers (74,158) were surveyed and divided into seven age groups (1–17, 18–29, 30–39, 40–49, 59–59, 60–69, and 70+ years old), among whom 14,275 were identified as having antibodies to SARS-CoV-2. The average percent seropositive in Russia was 17.8% (IQR: 8.8–23.2). The largest proportion was found among children under 17 years old (21.6% (IQR: 13.1–31.7). In the remaining groups, seroprevalence ranged from 15.6% (IQR: 8–21.1) to 18.0% (IQR: 13.4–22.6). During monitoring, three (immune) response groups were found: (A) groups with a continuous increase in the proportion of seropositive; (B) those with a slow rate of increase in seroprevalence; and (C) those with a two-phase curve, wherein the initial increase was replaced by a decrease in the percentage of seropositive individuals. A significant correlation was revealed between the number of COVID-19 convalescents and contact persons, and between the number of contacts and healthy seropositive volunteers. Among the seropositive volunteers, more than 93.6% (IQR: 87.1–94.9) were asymptomatic. The results show that the COVID-19 pandemic is accompanied by an increase in seroprevalence, which may be important for the formation of herd immunity.

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Prevalence and factors related to infection and mortality due to COVID-19 among patients of Shohada Ghaen Hospital, Ghaen, Iran, 2020

Journal of Birjand University of Medical Sciences ◽

10.32592/jbirjandunivmedsci.2021.28.4.106 ◽

2021 ◽

pp. 375-384

Keyword(s):

Risk Factors ◽

Clinical Symptoms ◽

Age Groups ◽

The Elderly ◽

Shortness Of Breath ◽

Hospital Data ◽

Chi Square ◽

Exact Test ◽

Risk Of Death ◽

First Case

Background and Aims: Coronavirus disease 2019 (COVID-19) is an emerging disease, whose first case was reported in December 2019, and rapidly affected the world. Therefore, the present study was conducted to investigate the frequency and factors associated with morbidity and mortality due to COVID -19 in Ghaen, Iran. Materials and Methods: This retrospective descriptive-analytical study used the information sources of the portal of Shohada Ghaen Hospital, Gaen, Iran, from March 2020 to December 2021, which was collected from 1,124 patients with suspected respiratory infection referring to the hospital. Data using Chi-square and Fisher's exact test for univariate relationships. Moreover, two-way logistic regression was used to investigate the causal relationships, and P<0.05 was considered statistically significant. Results: In this study, the mean age of participants (n=1,124) was obtained at 51.6±24.5 years, and 546 (48.6%) subjects had a positive COVID-19 test by reverse transcription polymerase chain reaction, among whom 65 (11.9%) cases passed away. Clinical symptoms of body aches, coughs, diarrhea, and shortness of breath were associated with a positive COVID-19 test. It was also revealed that habitat, diabetes, cardiovascular and lung diseases, age, and job were risk factors of COVID-19 infection, and hospitalization in the ICU and age were identified as risk factors for COVID-19-caused death (P<0.05). Conclusion: In the present study, cough and shortness of breath were found to be the most frequent symptoms among patients and deceased individuals. Since these symptoms may be associated with a worse prognosis, they require the special attention of medical staff. The findings of this study also showed that the elderly were more at risk of death from this disease than other age groups, which increased the need for more education and attention to this group of society.

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Assessment of Population Immunity to SARS-CoV-2 Virus in the Rostov Region

Problems of Particularly Dangerous Infections ◽

10.21055/0370-1069-2020-4-117-124 ◽

2021 ◽

pp. 117-124

Author(s):

A. Yu. Popova ◽

E. B. Ezhlova ◽

A. A. Mel’nikova ◽

A. K. Noskov ◽

E. V. Kovalev ◽

...

Keyword(s):

Herd Immunity ◽

Age Groups ◽

Incidence Rates ◽

The State ◽

Scientific Center ◽

Education Professionals ◽

Humoral Immune ◽

Population Immunity ◽

Rostov Region ◽

High Level

By August 2020, more than 850000 cases of new coronavirus infection (COVID-19) caused by SARSCoV-2 were confirmed in the Russian Federation, with the Rostov Region as one of the ten most affected regions in Russia. The spread of the disease is largely determined by the state of population immunity in a certain area. Our research focuses on specific humoral immune response and estimates the level of herd immunity to SARS-CoV-2 virus among the population of the Rostov Region.Materials and methods. The study involved 3,048 people; the volunteers participating in the study were divided into seven age groups. The content of antibodies to SARS-CoV-2 was determined applying ELISA using a kit for the analysis of human serum or blood plasma for the presence of specific IgG to the nucleocapsid of the SARS-CoV-2 virus, manufactured by the State Scientific Center of Applied Microbiology and Biotechnology (Obolensk) in accordance with the instructions for use.Results and discussion. The assessment of seroprevalence to SARS-CoV-2 in the Rostov Region showed that the proportion of people positive for IgG to the new coronavirus was 16.5 %, the range of seropositive individuals in the general population was between 13.9 % and 19.1 % (p<0.05). There were no significant gender differences in the degree of seroprevalence with a positive result registered in 16.6 % of women and 16.5 % of men. A high level of humoral immunity to SARS-CoV-2 was established in individuals aged 1–17 against the background of low incidence rates, which may indicate the dominance of asymptomatic forms of the disease in this age group. The highest level of seropositivity was found in preschool children (33.6 %), students (29.3 %), employees (17.3 %), and education professionals (15.3 %).

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Characteristic of herd immunity among the population of Stavropol region amid the COVID-19 epidemic

Journal Infectology ◽

10.22625/2072-6732-2021-13-4-79-89 ◽

2021 ◽

Vol 13 (4) ◽

pp. 79-89

Author(s):

A. Yu. Popova ◽

E. B. Ezhlova ◽

A. A. Melnikova ◽

V. S. Smirnov ◽

L. V. Lyalina ◽

...

Keyword(s):

Herd Immunity ◽

Age Groups ◽

Population Level ◽

Fold Increase ◽

Disease Spread ◽

Steady Increase ◽

Epidemic Process ◽

Population Immunity ◽

First Case ◽

Asymptomatic Volunteers

Introduction. The first pandemic in the 21st century, caused by the pathogenic representative of the coronavirus SARS-CoV-2, began in the Chinese city of Wuhan, where the first outbreak of coronavirus pneumonia was recorded in December 2019. The disease spread so quickly around the world that already on February 11, 2020, WHO was forced to declare a pandemic of the “coronavirus disease 2019” COVID-19. The first case of COVID-19 in the Stavropol Territory was registered on March 20, 2020, and three weeks later, starting from the 15th week of the year, a steady increase in the incidence began, which lasted until the 52nd week. During the study period, the incidence increased from 21.1 to 28.3 per hundred thousand of the population. Growth 1.3 times.Purpose: to determine the dynamics of population immunity among the population of the Stavropol Territory in 2020-2021. during the period of an epidemic increase in the incidence of COVID-19. Materials and methods. The SARS-CoV-2 study was carried out according to a unified methodology within the framework of the program for assessing the population immunity of the population of the Russian Federation, developed by Rospotrebnadzor with the participation of the St. Pasteur. In total, 2688 people were examined, divided into 7 age groups. In the examined individuals, the level of specific IgG to the SARS-CoV-2 nucleocapsid was determined by the enzyme immunoassay.Results. The level of seroprevalence among residents of the Stavropol Territory was 9.8%. The largest proportion of seropositive individuals was found in the age groups 1-6 and 7-13 years old (19.2% and 19.7%, respectively). Seroprevalence had no gender differences and ranged from 9.3% to 10.8%. When assessing the distribution of the proportion of seropositive persons in different geographic territories of the region, it was found that the maximum proportion was found in the Kochubeevsky district (23.1%), the minimum in Kislovodsk (7.7%). Among convalescents, the content of specific antibodies to SARS-CoV-2 was noted in 73.3%, which is 7.8 times higher than the average population level. When conducting seromonitoring in the 2nd half of 2020, a 10-fold increase in seroprevalence was recorded, accompanied by a decrease in incidence from the 5th week of 2021. Among asymptomatic volunteers in whom SARS-CoV-2 RNA was detected by the polymerase chain reaction, antibody titers to viruses were found in 78.6%, which corresponds to the seroprevalence of convalescents. The proportion of seropositive persons among those who have come into contact with COVID-19 patients was 16.4%, (1.8 times higher than the average for the population). Out of 262 seroprevalent volunteers, the asymptomatic form of SARS-CoV-2 was detected in 92% of the examined, which indicates a significant role of the number of asymptomatic forms of infection in the epidemic process of COVID-19.Conclusion. The results of assessing the population immunity of the population of the Stavropol Territory indicate that it has not yet reached the threshold level at which a decrease in the intensity of the COVID-19 epidemic process can be expected.

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Assessment of the Herd Immunity to SARS-CoV-2 among the Population of the Leningrad Region during the COVID-19 Epidemic

Problems of Particularly Dangerous Infections ◽

10.21055/0370-1069-2020-3-114-123 ◽

2020 ◽

pp. 114-123

Author(s):

A. Yu. Popova ◽

E. B. Ezhlova ◽

A. A. Mel’nikova ◽

O. A. Historik ◽

O. S. Mosevich ◽

...

Keyword(s):

Herd Immunity ◽

Significant Proportion ◽

Maximum Level ◽

Leningrad Region ◽

Scientific Center ◽

Epidemic Process ◽

First Case ◽

Applied Microbiology ◽

Instructions For Use ◽

The Unemployed

The first case of COVID-19 was registered in the Leningrad Region on March 13, 2020. The period of increasing intensity of the epidemic process lasted 8 weeks. One month after reaching the maximum incidence rate, a study was organized to determine seroprevalence to COVID-19 among the population of the Region.Objective of the study was to determine the level and structure of community immunity to SARS-CoV-2 virus in the population of the Leningrad Region in the period of intensive COVID-19 transmission.Materials and methods. The work was carried out within the framework of the Rospotrebnadzor project on assessment of community immunity to the SARS-CoV-2 virus in the population of the Russian Federation. The content of antibodies to SARS-CoV-2 was determined applying ELISA using a kit for the analysis of human serum or blood plasma for the presence of specific IgG to the nucleocapsid of the SARS-CoV-2 virus , manufactured by the State Scientific Center of Applied Microbiology and Biotechnology (Obolensk) in accordance with the instructions for use.Results and discussion. The study has showed that the herd immunity of the population of the Leningrad Region was 20.7 %. The maximum level has been established in children 1–6 years old (42.3 %) and people over 70 years old (29.0 %). The highest level of seropositivity, except for children and older people, was found among the unemployed (25.1 %). The lowest level of seroprevalence was detected in civil servants (12.8 %) and military personnel (16.7 %). It has been shown that the risk of infection increases by 1.5 times in case of contacts with COVID-19 patients. After exposure to COVID-19 virus, antibodies are produced in 82.1 % of the cases. In individuals with a positive PCR test result obtained earlier, antibodies are detected in 82.8 % of cases. The share of asymptomatic forms among seropositive residents of the Leningrad Region was 86.9 %. The results of assessing the herd immunity to SARS-CoV-2 in the population of the Leningrad Region indicate that during the period of intensive COVID-19 transmission, an average level of seroprevalence was formed. A significant proportion of asymptomatic forms of infection characterizes the high intensity of the latently developing epidemic process. The results obtained should be taken into account when organizing preventive measures, including vaccination, and predicting morbidity rates.

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