ACHIEVEMENT OF MAXIMAL SARS-CoV-2 COLLECTIVE IMMUNITY AMONG THE TAJIK POPULATION BY MARCH 2022

Despite all efforts of the world community, the COVID-19 pandemic remains one of the main epidemiological challenges of our time. Even with its widespread distribution, the infection may have certain local features due to social, geographic, and climatic factors. Objective(s): to study collective immunity to SARS-CoV-2 in the population of the Republic of Tajikistan. A cross-sectional, randomized study of herd immunity was carried out according to a program developed by Rospotrebnadzor and the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The ethics committees of the corresponding entities approved the study: Tajik Ministry of Health and Social Protection;and the St. Petersburg Pasteur Institute (Russia). Based on questionnaire results, 4,022 people were selected, representing 0.15% (95% CI: 0.14-0.15) of the total population randomized by age and region. In subsequent laboratory analysis, 3682 people took part. The distribution and quantitative content of antibodies (Abs) to viral nucleocapsid (N Ag) and receptor binding domain (RBD Ag) were determined by ELISA. When questioned, a history of SARS-CoV-2 vaccination was indicated by 69.7% (95% CI: 68.2-71.2) of the volunteer cohort. Vector vaccines were most frequently used (50.6%;95% CI: 48.7-52.5), with whole-virion inactivated preparations in second place (23.0%: 95% CI: 21.4-26.6) and mRNA vaccines in third place (21.0%;95% CI:19.4-22.6). The cohort (n = 3682) featured 27.5% men and 72.5% women. The overall seroprevalence was 98.5% (95% CI: 97.7-99.2) in men and 99.4% (95% CI: 99.0-99.6) in women (differences statistically insignificant). Overall seroprevalence in the cohort was 99.2% (95% CI: 98.8-99.4) and ranged from 97.2 to 100% in certain subgroups. Asymptomatic seropositivity in the whole cohort was 98.4% (95% CI: 97.6-99.1). As a result of a mandatory vaccination program introduced in Tajikistan under a COVID-19 Emergency Project, the level of herd immunity among vaccinated individuals reached 99.5% (95% CI: 99.1-99.7), which is similar to the level reached in the cohort as a whole. The epidemic situation that developed in Tajikistan by mid-March 2022 was characterized by an almost absolute level of herd immunity, as evidenced by an absence of detected overt COVID-19 cases since the end of February (2022).Copyright © Popova A.Yu. et al., 2023 The article can be used under the Creative Commons Attribution 4.0 License.

Cytokine Profiling in Different SARS-CoV-2 Genetic Variants.

This study is a successor of our previous work concerning changes in the chemokine profile in infection that are associated with different SARS-CoV-2 genetic variants. The goal of our study was to take into account both the virus and the host immune system by assessing concentrations of cytokines in patients infected with different SARS-CoV-2 variants (ancestral Wuhan strain, Alpha, Delta and Omicron). Our study was performed on 340 biological samples taken from COVID-19 patients and healthy donors in the timespan between May 2020 and April 2022. We performed genotyping of the virus in nasopharyngeal swabs, which was followed by assessment of cytokines' concentration in blood plasma. We noted that out of nearly 30 cytokines, only four showed stable elevation independently of the variant (IL-6, IL-10, IL-18 and IL-27), and we believe them to be 'constant' markers for COVID-19 infection. Cytokines that were studied as potential biomarkers lose their diagnostic value as the virus evolves, and the specter of potential targets for predictive models is narrowing. So far, only four cytokines (IL-6, IL-10, IL-18, and IL-27) showed a consistent rise in concentrations independently of the genetic variant of the virus. Although we believe our findings to be of scientific interest, we still consider them inconclusive; further investigation and comparison of immune responses to different variants of SARS-CoV-2 is required.

T HELPER CELL SUBSETS AND RELATED TARGET CELLS IN ACUTE COVID-19.

Current review presents a brief overview of the immune system dysregulation during acute COVID-19 and illustrates the main alterations in peripheral blood CD4+ T-cell (Th) subsets as well as related target cells. Effects of dendritic cell dysfunction induced by SARS-CoV-2 exhibited decreased expression of cell-surface HLA-DR, CCR7 as well as co-stimulatory molecules CD80 and CD86, suggesting reduced antigen presentation, migratory and activation capacities of peripheral blood dendritic cells. SARS-CoV-2-specific Th cells could be detected as early as days 2-4 post-symptom onset, whereas the prolonged lack of SARS-CoV-2-specific Th cells was associated with severe and/or poor COVID-19 outcome. Firstly, in acute COVID-19 the frequency of Th1 cell was comparable with control levels, but several studies have reported about upregulated inhibitory immune checkpoint receptors and exhaustion-associated molecules (TIM3, PD-1, BTLA, TIGIT etc.) on circulating CD8+ T-cells and NK-cells, whereas the macrophage count was increased in bronchoalveolar lavage (BAL) samples. Next, type 2 immune responses are mediated mainly by Th2 cells, and several studies have revealed a skewing towards dominance of Th2 cell subset in peripheral blood samples from patients with acute COVID-19. Furthermore, the decrease of circulating main Th2 target cells - basophiles and eosinophils - were associated with severe COVID-19, whereas the lung tissue was enriched with mast cells and relevant mediators released during degranulation. Moreover, the frequency of peripheral blood Th17 cells was closely linked to COVID-19 severity, so that low level of Th17 cells was observed in patients with severe COVID-19, but in BAL the relative number of Th17 cells as well as the concentrations of relevant effector cytokines were dramatically increased. It was shown that severe COVID-19 patients vs. healthy control had higher relative numbers of neutrophils if compared, and the majority of patients with COVID-19 had increased frequency and absolute number of immature neutrophils with altered ROS production. Finally, the frequency of Tfh cells was decreased during acute COVID-19 infection. Elevated count of activated Tfh were found as well as the alterations in Tfh cell subsets characterized by decreased "regulatory" Tfh1 cell and increased "pro-inflammatory" Tfh2 as well as Tfh17 cell subsets were revealed. Descriptions of peripheral blood B cells during an acute SARS-CoV-2 infection werev reported as relative B cell lymphopenia with decreased frequency of "naive" and memory B cell subsets, as well as increased level of CD27hiCD38hiCD24- plasma cell precursors and atypical CD21low B cells. Thus, the emerging evidence suggests that functional alterations occur in all Th cell subsets being linked with loss-of-functions of main Th cell subsets target cells. Furthermore, recovered individuals could suffer from long-term immune dysregulation and other persistent symptoms lasting for many months even after SARS-CoV-2 elimination, a condition referred to as post-acute COVID-19 syndrome.Copyright © 2022 Saint Petersburg Pasteur Institute. All rights reserved.

ATR-FTIR spectrum analysis of plasma samples for rapid identification of recovered COVID-19 individuals.

The development of fast, cheap and reliable methods to determine seroconversion against infectious agents is of great practical importance. In the context of the COVID-19 pandemic, an important issue is to study the rate of formation of the immune layer in the population of different regions, as well as the study of the formation of post-vaccination immunity in individuals after vaccination. Currently, the main method for this kind of research is enzyme immunoassay (ELISA, enzyme-linked immunosorbent assay). This technique is sufficiently sensitive and specific, but it requires significant time and material costs. We investigated the applicability of attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy associated with machine learning in blood plasma to detect seroconversion against SARS-CoV-2. The study included samples of 60 patients. Clear spectral differences in plasma samples from recovered COVID-19 patients and conditionally healthy donors were identified using multivariate and statistical analysis. The results showed that ATR-FTIR spectroscopy, combined with principal components analysis (PCA) and linear discriminant analysis (LDA) or artificial neural network (ANN), made it possible to efficiently identify specimens from recovered COVID-19 patients. We built classification models based on PCA associated with LDA and ANN. Our analysis led to 87% accuracy for PCA-LDA model and 91% accuracy for ANN, respectively. Based on this proof-of-concept study, we believe this method could offer a simple, label-free, cost-effective tool for detecting seroconversion against SARS-CoV-2. This approach could be used as an alternative to ELISA.

Prevalence of HIV and Viral Hepatitis Markers among Healthcare Workers in the Republic of Guinea.

Healthcare workers are much more likely to be infected with HIV and hepatitis viruses compared to the general population. Although healthcare workers are more aware of HIV and hepatitis viruses, several countries in Africa lack a comprehensive grasp of disease routes and transmission risks. The aim of this study was to assess the prevalence of the serological and molecular biological markers of HIV and viral hepatitis among healthcare workers in the Republic of Guinea. The study material was 74 blood serum samples collected from healthcare workers who received additional training at the Institute of Applied Biological Research of Guinea (IRBAG, Kindia, Republic of Guinea). The markers examined included HBsAg, HBeAg, anti-HBs IgG, anti-HBcore IgG, anti-HCV qualitative determination, anti-HEV IgM and IgG, anti-HAV IgM and IgG, and anti-HIV. For viral DNA and RNA detection, nucleic acids were extracted from blood serum, and viral presence was inferred using real-time PCR with hybridization fluorescence detection. A high prevalence of viral hepatitis B markers was shown, and significantly fewer cases of viral hepatitis C and HIV were detected. Almost all examined medical workers had anti-HAV IgG antibodies, but no antibodies to hepatitis E virus. Apparently, the identified markers depend on the general prevalence of certain pathogens in the region and are associated with the traditions and characteristics of the country's residents.

T HELPER CELL SUBSETS AND RELATED TARGET CELLS IN ACUTE COVID-19

Current review presents a brief overview of the immune system dysregulation during acute COVID-19 and illustrates the main alterations in peripheral blood CD4+ T-cell (Th) subsets as well as related target cells. Effects of dendritic cell dysfunction induced by SARS-CoV-2 exhibited decreased expression of cell-surface HLA-DR, CCR7 as well as co-stimulatory molecules CD80 and CD86, suggesting reduced antigen presentation, migratory and activation capacities of peripheral blood dendritic cells. SARS-CoV-2-specific Th cells could be detected as early as days 2–4 post-symptom onset, whereas the prolonged lack of SARS-CoV-2-specific Th cells was associated with severe and/or poor COVID-19 outcome. Firstly, in acute COVID-19 the frequency of Th1 cell was comparable with control levels, but several studies have reported about upregulated inhibitory immune checkpoint receptors and exhaustion-associated molecules (TIM3, PD-1, BTLA, TIGIT etc.) on circulating CD8+ T-cells and NK-cells, whereas the macrophage count was increased in bronchoalveolar lavage (BAL) samples. Next, type 2 immune responses are mediated mainly by Th2 cells, and several studies have revealed a skewing towards dominance of Th2 cell subset in peripheral blood samples from patients with acute COVID-19. Furthermore, the decrease of circulating main Th2 target cells — basophiles and eosinophils — were associated with severe COVID-19, whereas the lung tissue was enriched with mast cells and relevant mediators released during degranulation. Moreover, the frequency of peripheral blood Th17 cells was closely linked to COVID-19 severity, so that low level of Th17 cells was observed in patients with severe COVID-19, but in BAL the relative number of Th17 cells as well as the concentrations of relevant effector cytokines were dramatically increased. It was shown that severe COVID-19 patients vs. healthy control had higher relative numbers of neutrophils if compared, and the majority of patients with COVID-19 had increased frequency and absolute number of immature neutrophils with altered ROS production. Finally, the frequency of Tfh cells was decreased during acute COVID-19 infection. Elevated count of activated Tfh were found as well as the alterations in Tfh cell subsets characterized by decreased "regulatory” Tfh1 cell and increased "pro-inflammatory” Tfh2 as well as Tfh17 cell subsets were revealed. Descriptions of peripheral blood B cells during an acute SARS-CoV-2 infection werev reported as relative B cell lymphopenia with decreased frequency of "naïve” and memory B cell subsets, as well as increased level of CD27hiCD38hiCD24– plasma cell precursors and atypical CD21low B cells. Thus, the emerging evidence suggests that functional alterations occur in all Th cell subsets being linked with loss-of-functions of main Th cell subsets target cells. Furthermore, recovered individuals could suffer from long-term immune dysregulation and other persistent symptoms lasting for many months even after SARS-CoV-2 elimination, a condition referred to as post-acute COVID-19 syndrome.

Heterogenous CD8+ T Cell Maturation and 'Polarization' in Acute and Convalescent COVID-19 Patients.

BACKGROUND: The adaptive antiviral immune response requires interaction between CD8+ T cells, dendritic cells, and Th1 cells for controlling SARS-CoV-2 infection, but the data regarding the role of CD8+ T cells in the acute phase of COVID-19 and post-COVID-19 syndrome are still limited. METHODS: . Peripheral blood samples collected from patients with acute COVID-19 (n = 71), convalescent subjects bearing serum SARS-CoV-2 N-protein-specific IgG antibodies (n = 51), and healthy volunteers with no detectable antibodies to any SARS-CoV-2 proteins (HC, n = 46) were analyzed using 10-color flow cytometry. RESULTS: Patients with acute COVID-19 vs. HC and COVID-19 convalescents showed decreased absolute numbers of CD8+ T cells, whereas the frequency of CM and TEMRA CD8+ T cells in acute COVID-19 vs. HC was elevated. COVID-19 convalescents vs. HC had increased naïve and CM cells, whereas TEMRA cells were decreased compared to HC. Cell-surface CD57 was highly expressed by the majority of CD8+ T cells subsets during acute COVID-19, but convalescents had increased CD57 on 'naïve', CM, EM4, and pE1 2-3 months post-symptom onset. CXCR5 expression was altered in acute and convalescent COVID-19 subjects, whereas the frequencies of CXCR3+ and CCR4+ cells were decreased in both patient groups vs. HC. COVID-19 convalescents had increased CCR6-expressing CD8+ T cells. Moreover, CXCR3+CCR6- Tc1 cells were decreased in patients with acute COVID-19 and COVID-19 convalescents, whereas Tc2 and Tc17 levels were increased compared to HC. Finally, IL-27 negatively correlated with the CCR6+ cells in acute COVID-19 patients. CONCLUSIONS: We described an abnormal CD8+ T cell profile in COVID-19 convalescents, which resulted in lower frequencies of effector subsets (TEMRA and Tc1), higher senescent state (upregulated CD57 on 'naïve' and memory cells), and higher frequencies of CD8+ T cell subsets expressing lung tissue and mucosal tissue homing molecules (Tc2, Tc17, and Tc17.1). Thus, our data indicate that COVID-19 can impact the long-term CD8+ T cell immune response.

A Comparative Study of the Plasma Chemokine Profile in COVID-19 Patients Infected with Different SARS-CoV-2 Variants.

BACKGROUND: Infection caused by SARS-CoV-2 mostly affects the upper and lower respiratory tracts and causes symptoms ranging from the common cold to pneumonia with acute respiratory distress syndrome. Chemokines are deeply involved in the chemoattraction, proliferation, and activation of immune cells within inflammation. It is crucial to consider that mutations within the virion can potentially affect the clinical course of SARS-CoV-2 infection because disease severity and manifestation vary depending on the genetic variant. Our objective was to measure and assess the different concentrations of chemokines involved in COVID-19 caused by different variants of the virus. METHODS: We used the blood plasma of patients infected with different variants of SARS-CoV-2, i.e., the ancestral Wuhan strain and the Alpha, Delta, and Omicron variants. We measured the concentrations of 11 chemokines in the samples: CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1ß, CCL7/MCP-3, CCL11/Eotaxin, CCL22/MDC, CXCL1/GROα, CXCL8/IL-8, CXCL9/MIG, CXCL10/IP-10, and CX3CL1/Fractalkine. RESULTS: We noted a statistically significant elevation in the concentrations of CCL2/MCP-1, CXCL8/IL-8, and CXCL1/IP-10 independently of the variant, and a drop in the CCL22/MDC concentrations. CONCLUSIONS: The chemokine concentrations varied significantly depending on the viral variant, leading us to infer that mutations in viral proteins play a role in the cellular and molecular mechanisms of immune responses.

T HELPER CELL SUBSETS AND RELATED TARGET CELLS IN ACUTE COVID-19

Current review presents a brief overview of the immune system dysregulation during acute COVID-19 and illustrates the main alterations in peripheral blood CD4+ T-cell (Th) subsets as well as related target cells. Effects of dendritic cell dysfunction induced by SARS-CoV-2 exhibited decreased expression of cell-surface HLA-DR, CCR7 as well as co-stimulatory molecules CD80 and CD86, suggesting reduced antigen presentation, migratory and activation capacities of peripheral blood dendritic cells. SARS-CoV-2-specific Th cells could be detected as early as days 2–4 post-symptom onset, whereas the prolonged lack of SARS-CoV-2-specific Th cells was associated with severe and/or poor COVID-19 outcome. Firstly, in acute COVID-19 the frequency of Th1 cell was comparable with control levels, but several studies have reported about upregulated inhibitory immune checkpoint receptors and exhaustion-associated molecules (TIM3, PD-1, BTLA, TIGIT etc.) on circulating CD8+ T-cells and NK-cells, whereas the macrophage count was increased in bronchoalveolar lavage (BAL) samples. Next, type 2 immune responses are mediated mainly by Th2 cells, and several studies have revealed a skewing towards dominance of Th2 cell subset in peripheral blood samples from patients with acute COVID-19. Furthermore, the decrease of circulating main Th2 target cells — basophiles and eosinophils — were associated with severe COVID-19, whereas the lung tissue was enriched with mast cells and relevant mediators released during degranulation. Moreover, the frequency of peripheral blood Th17 cells was closely linked to COVID-19 severity, so that low level of Th17 cells was observed in patients with severe COVID-19, but in BAL the relative number of Th17 cells as well as the concentrations of relevant effector cytokines were dramatically increased. It was shown that severe COVID-19 patients vs. healthy control had higher relative numbers of neutrophils if compared, and the majority of patients with COVID-19 had increased frequency and absolute number of immature neutrophils with altered ROS production. Finally, the frequency of Tfh cells was decreased during acute COVID-19 infection. Elevated count of activated Tfh were found as well as the alterations in Tfh cell subsets characterized by decreased “regulatory” Tfh1 cell and increased “pro-inflammatory” Tfh2 as well as Tfh17 cell subsets were revealed. Descriptions of peripheral blood B cells during an acute SARS-CoV-2 infection werev reported as relative B cell lymphopenia with decreased frequency of “naïve” and memory B cell subsets, as well as increased level of CD27hiCD38hiCD24– plasma cell precursors and atypical CD21low B cells. Thus, the emerging evidence suggests that functional alterations occur in all Th cell subsets being linked with loss-of-functions of main Th cell subsets target cells. Furthermore, recovered individuals could suffer from long-term immune dysregulation and other persistent symptoms lasting for many months even after SARS-CoV-2 elimination, a condition referred to as post-acute COVID-19 syndrome.

SARS-CoV-2 herd immunity of the Kyrgyz population in 2021.

In the fight against coronavirus infection, control of the immune response is of decisive importance, an important component of which is the seroprevalence of antibodies to SARS-CoV-2. Immunity to SARS-CoV-2 is formed either naturally or artificially through vaccination. The purpose of this study was to assess the seroprevalence of antibodies to SARS-CoV-2 in the population of Kyrgyzstan. A cross-sectional randomized study of seroprevalence was carried out according to a program developed by Rospotrebnadzor and the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The ethics committees of the Association of Preventive Medicine (Kyrgyzstan) and the St. Petersburg Pasteur Institute (Russia) approved the study. Volunteers (9471) were recruited, representing 0.15% (95% CI 0.14-0.15) of the total population, randomized by age and region. Plasma antibodies (Abs) to the nucleocapsid antigen (Nag) were determined. In vaccinated individuals, Abs to the SARS-CoV-2 receptor-binding domain antigen (RBDag) were determined. Differences were considered statistically significant at p < 0.05. The SARS-CoV-2 Nag Ab seroprevalence was 48.7% (95% CI 47.7-49.7), with a maximum in the 60-69 age group [59.2% (95% CI 56.6-61.7)] and a minimum in group 1-17 years old [32.7% (95 CI: 29.4-36.1)]. The highest proportion of seropositive individuals was in the Naryn region [53.3% (95% CI 49.8-56.8)]. The lowest share was in Osh City [38.1% (95% CI 32.6-43.9)]. The maximum SARS-CoV-2 Nag seropositivity was found in the health-care sector [57.1% (95% CI 55.4-58.8)]; the minimum was seen among artists [38.6% (95% CI 26.0-52.4)]. Asymptomatic SARS-CoV-2 Nag seropositivity was 77.1% (95% CI 75.6-78.5). Vaccination with Sputnik V or Sinopharm produced comparable Ab seroprevalence. SARS-CoV-2 Nag seropositivity in the Kyrgyz population was 48.75% (95% CI 47.7-49.7), with the mass vaccination campaign undoubtedly benefitting the overall situation.

POST-VACCINATION IMMUNITY PHENOTYPES UPON USAGE OF EpiVacCorona VACCINE IN THE PERSONS WHO SUFFERED COVID-19

The dominance of reliably immunized population is a fundamental factor in prevention of COVID-19 pandemia, with immune prophylaxis taking a dominant position. Due to lack of clear data on the intensity of specific immunity after a new coronavirus infection, consolidation of immunological memory by vaccination becomes the urgent task, in order to exclude the risk of re-involvement of previously ill patients into the epidemic process. Meanwhile, many questions related to vaccination of COVID-19 survivors do not get distinct answers. To study the features of immune response, using a vaccine based on SARS-CoV-2 peptide antigens (EpiVacCorona), we monitored 81 participants. The inclusion criteria were data confirming COVID-19 in the anamnesis (medical documentation), low levels or absence of antibodies to the SARS-CoV-2 nucleocapsid protein, and negative PCR tests for SARS-CoV-2. When assessing the data of post-vaccinal immunity checked 21 days after 1st dose of the vaccine, the patients were divided into 2 groups: those who did not respond, and those who developed the immune response. In order to identify possible reasons for different phenotypic patterns of humoral response to vaccination, a comparative analysis of B lymphocyte indexes was carried out in these groups. Absolute counts, subpopulation composition and activation potential of peripheral blood B lymphocytes were determined by flow cytofluorometry using appropriate labeled monoclonal antibodies purchased from Beсkman Coulter. Comparative analysis of B lymphocyte indexes on the day of first vaccination showed that the persons who did not respond to the vaccine had smaller counts of circulating B cells, i.e., both percentage and absolute cell numbers, than in comparison group, as well as changed ratio of B1-to-B2 subpopulations. After administration of the first vaccine dose (by day +21), in alternative variant of the antibody response to V1, the differences in the parameters of B cells were presented as a smaller percentage and absolute numbers of regulatory B lymphocytes in non-responding participants. Moreover, the contents of minor B cell subpopulations were decreased in the non-responding group than in the comparison group, thus affecting the values of the B1:B2 ratio. In general, the presented data demonstrate that the absence of secondary immune response to antigens of the SARS-CoV-2 peptide vaccine could be is associated with altered differentiation of B1 and B2 subpopulations, B regulatory lymphocytes, B memory cells.

Alterations in B Cell and Follicular T-Helper Cell Subsets in Patients with Acute COVID-19 and COVID-19 Convalescents

Background. Humoral immunity requires interaction between B cell and T follicular helper cells (Tfh) to produce effective immune response, but the data regarding a role of B cells and Tfh in SARS-CoV-2 defense are still sparse. Methods. Blood samples from patients with acute COVID-19 (n = 64), convalescents patients who had specific IgG to SARS-CoV-2 N-protein (n = 55), and healthy donors with no detectable antibodies to any SARS-CoV-2 proteins (HC, n = 44) were analyses by multicolor flow cytometry. Results. Patients with acute COVID-19 showed decreased levels of memory B cells subsets and increased proportion plasma cell precursors compared to HC and COVID-19 convalescent patients, whereas for the latter the elevated numbers of virgin naïve, Bm2′ and “Bm3+Bm4” was found if compared with HC. During acute COVID-19 CXCR3+CCR6− Tfh1-like cells were decreased and the levels of CXCR3−CCR6+ Tfh17-like were increased then in HC and convalescent patients. Finally, COVID-19 convalescent patients had increased levels of Tfh2-, Tfh17- and DP Tfh-like cells while comparing their amount with HC. Conclusions. Our data indicate that COVID-19 can impact the humoral immunity in the long-term.

REVEALING MEASLES CASES IN VIETNAM DURING THE SPREAD OF A NEW CORONAVIRUS INFECTION

Introduction. According to the WHO Strategic Plan, five out of six geographical regions were expected to achieve measles elimination by 2020, among which is the Western Pacific Region (WPR), which includes the Socialist Republic of Vietnam (VNM). In 2019, 14 156 measles cases were detected in Vietnam, which significantly exceeds the level required to achieve its elimination (less than 1 case per 1 million population). Analyzing the causes of the ongoing measles virus circulation in diverse global regions is very important. It is also important to assess a potential impact on the measles incidence due to anti-epidemic measures aimed at combating the COVID-19 pandemic. This research is devoted to revealation measles cases in South Vietnam within the period covering January 2020 to March 2021. Materials and methods. 799 samples of blood sera obtained from different territories of South Vietnam in 2020-2021 were examined for IgM antibodies against measles virus using the Anti-Measles Virus ELISA (IgM) test system (Euroimmun, Germany). The presence of IgM measles virus antibodies in the blood serum was assessed as an acute measles infection. Results. The measles virus was actively circulating in South Vietnam in the first months of 2020. Residents of large cities and industrial centers were mainly involved in the epidemic process. Measles spread mainly among unvaccinated (71.58%) subjects, or who was unaware of vaccinations (25.48%), but also among those who were vaccinated (2.12%) and revaccinated (0.64%). The absolute majority of cases (71%) affected children under the age of three, with a predominance of those at the first year of life. Among the latter, 48% were children aged 7-9 months old. In March-April 2020, there was a sharp decrease in the number of measles cases in South Vietnam, down to a sporadic level (from May 2020 to March 2021). This is probably due to the anti-epidemic measures that were carried out in the VNM in order to limit the spread of COVID-19. Consequently, after the restrictions are lifted, we can expect an increase in the measles incidence in VNM.

Changes in Anti-SARS-CoV-2 IgG Subclasses over Time and in Association with Disease Severity.

IgG is the most prominent marker of post-COVID-19 immunity. Not only does this subtype mark the late stages of infection, but it also stays in the body for a timespan of at least 6 months. However, different IgG subclasses have different properties, and their roles in specific anti-COVID-19 responses have yet to be determined. We assessed the concentrations of IgG1, IgG2, IgG3, and IgG4 against different SARS-CoV-2 antigens (N protein, S protein RBD) using a specifically designed method and samples from 348 COVID-19 patients. We noted a statistically significant association between severity of COVID-19 infection and IgG concentrations (both total and subclasses). When assessing anti-N protein and anti-RBD IgG subclasses, we noted the importance of IgG3 as a subclass. Since it is often associated with early antiviral response, we presumed that the IgG3 subclass is the first high-affinity IgG antibody to be produced during COVID-19 infection.

Longitudinal Randomized Cohort Study of SARS-CoV-2 Antibody Seroprevalence in the St. Petersburg Population.

Introduction. Since the detection of the first COVID-19 patient, 2 years have passed, during which more than 287,862,000 people have fallen ill globally, of which about 1.9% died. The implementation of SARS-CoV-2 control programs required efforts from almost all countries. An important direction in the fight against COVID-19 has been the formation of herd immunity, the main tool for managing the pandemic. Study goal. The aim of the study was to assess the seroprevalence of antibodies (Abs) to SARS-CoV-2 nucleocapsid (Nc) and receptor binding domain (RBD) in the St. Petersburg population during the COVID-19 pandemic. Materials and methods. A longitudinal cohort randomized monitoring study of Ab seroprevalence (SARS-CoV-2 Nc, RBD) was organized and conducted according to a unified methodology developed by Rospotrebnadzor with the participation of the St. Petersburg Pasteur Institute. For this purpose, a cohort was formed of 1000 volunteers who participated in all five stages of seromonitoring. The cohort was divided into seven age groups: 1-17; 18-29; 30-39; 40-49; 50-59; 60-69; 70; and older (70+) years. Seropositivity levels (Nc, RBD) were assessed by quantitative and qualitative enzyme immunoassays. During the second year of monitoring, some volunteers were vaccinated with the GamCOVIDVac (84%) or EpiVacCorona (11.6%) vaccines approved in Russia. Statistical processing was carried out using Excel 2010. Confidence intervals for shares and percentages (95% CI) were calculated using the method of A. Wald and J. Wolfowitz with adjustment (A. Agresti, B.A. Coull). The statistical significance of differences was calculated by z-test, using the appropriate online calculator (p < 0.05) unless indicated. Results. There was a trend toward an increase in Nc seropositivity in stages 1-3 of seromonitoring, with a decrease in stages 4-5 among children and adults. The share of RBD seropositive steadily increased during all five stages of seromonitoring. The most frequent finding was low anti-RBD Abs levels (22.6-220 BAU/mL). High Ab levels were recorded statistically significantly less frequently. Asymptomatic forms were observed in 84-88% of SARS-CoV-2 seropositive volunteers. By the fifth stage of monitoring, this indicator significantly decreased to 69.8% (95% CI: 66.1-73.4). The monitoring revealed a statistically significant increase in anti-RBD Abs alongside a statistically significant decrease in the proportion of Nc seropositives. This dynamic was especially characteristic of persons vaccinated with GamCOVIDVac. Conclusion. Prior to the use of specific vaccines, a seroprevalence of anti-Nc Abs was noted. After the introduction of the GamCOVIDVac vaccine in adults, a decrease in the level of anti-Nc Abs was noted due to an increase in the proportion of RBD seropositive persons.

2019–2020 Measles in the Republic of Guinea: Epidemic features and herd immunity

Introduction. In connection with the Ebola epidemic in the West African countries, including the Republic of Guinea, a failure in implementing measles immunization program was noted. A proportion of measles seronegative subjects in 2017 was 52.4% of total examined individuals. In 2018, a high proportion of measles cases among children aged 1–5 years (61.6%) was identified. In order to stop the 2018 outbreak, the Supplemental Immunization Campaign was conducted in the Konakri and Nzerekore prefectures in the Republic of Guinea. The aim of this study was to examine the 2019–2020 measles epidemic situation and assess the measles population immunity in the Republic of Guinea. Materials and methods. Measles-specific antibodies were examined in 1697 blood serum samples collected from residents of different regions of the Republic of Guinea, aged from 7 months to 76 years, obtained in 2019–2020, and tested retrospectively. The ELISA test systems Anti-Measles Virus ELISA (IgM) Euroimmun and Anti-Measles Virus ELISA (IgG) Euroimmun (Germany) were used. The presence of serum IgM measles antibodies was considered as acute measles infection. Statistical analysis was performed using the software package Statistica 6.0. Results. Blood sera (n = 638) were tested for IgM-measles, and in 46.6% of cases the diagnosis was confirmed by laboratory tests. The biggest proportion of the total cases (61.6%) was found in children aged 1–4 years. The second most important age group was 5–9 years of age, the third is children under 1 year: 18.5% and 11.8% of the total number of patients, respectively. Measles infection was registered in vaccinated patients in 7.4% of the total number of laboratory-confirmed cases. 1059 subjects were examined for IgG measles antibody. The lowest seroprevalence rate was found among children under 4 years of age (47.8%). The highest (85.5%) was found among subjects of 40 years old and older. Conclusion. Measles in GR remains a poorly controlled infection. As in the previous years of observation (2017–2018), children under 5 years of age are the most vulnerable cohort of the population, despite the 2018 DI campaign conducted in a number of GR territories. More problems with the measles control in the Republic of Guinea are expected in the period from 2021, as along with the COVID-19 epidemic, Ebola is repeatedly registered in the country. The Republic of Guinea particularly requires assistance from the international community to implement the WHO measles elimination program on a global scale. © 2021 Saint Petersburg Pasteur Institute. All rights reserved.

A Novel Approach for COVID-19 Patient Condition Tracking: From Instant Prediction to Regular Monitoring.

Purpose: The aim of this research is to develop an accurate and interpretable aggregated score not only for hospitalization outcome prediction (death/discharge) but also for the daily assessment of the COVID-19 patient's condition. Patients and Methods: In this single-center cohort study, real-world data collected within the first two waves of the COVID-19 pandemic was used (27.04.2020-03.08.2020 and 01.11.2020-19.01.2021, respectively). The first wave data (1,349 cases) was used as a training set for the score development, while the second wave data (1,453 cases) was used as a validation set. No overlapping cases were presented in the study. For all the available patients' features, we tested their association with an outcome. Significant features were taken for further analysis, and their partial sensitivity, specificity, and promptness were estimated. Sensitivity and specificity were further combined into a feature informativeness index. The developed score was derived as a weighted sum of nine features that showed the best trade-off between informativeness and promptness. Results: Based on the training cohort (median age ± median absolute deviation 58 ± 13.3, females 55.7%), the following resulting score was derived: APTT (4 points), CRP (3 points), D-dimer (4 points), glucose (4 points), hemoglobin (3 points), lymphocytes (3 points), total protein (6 points), urea (5 points), and WBC (4 points). Internal and temporal validation based on the second wave cohort (age 60 ± 14.8, females 51.8%) showed that a sensitivity and a specificity over 90% may be achieved with an expected prediction range of more than 7 days. Moreover, we demonstrated high robustness of the score to the varying peculiarities of the pandemic. Conclusions: An extensive application of the score during the pandemic showed its potential for optimization of patient management as well as improvement of medical staff attentiveness in a high workload stress. The transparent structure of the score, as well as tractable cutoff bounds, simplified its implementation into clinical practice. High cumulative informativeness of the nine score components suggests that these are the indicators that need to be monitored regularly during the follow-up of a patient with COVID-19.

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

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.

Plasma cytokines in patients with COVID-19 during acute phase of the disease and following complete recovery

COVID-19, an infection caused by the new coronavirus SARS-CoV-2, is associated with a number of pathophysiological mechanisms, mobilizing a wide spectrum of biomolecules, mainly, cytokines. The purpose of this study was to evaluate levels of multiple cytokines in blood plasma from the patients with COVID-19 during acute phase of the disease, and upon complete recovery. Samples of peripheral blood plasma of 56 patients with COVID-19, 69 convalescents and 10 healthy individuals were examined. Concentrations of 46 molecules, such as IL-1α, IL-1β, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-12 (p40), IL-12 (p70), IL-13, IL-15, IL-17A/CTLA8, IL-17-E/IL-25, IL-17F, IL-18, IL-22, IL-27, IFNα2, IFNγ, TNFα, TNFβ/ Lymphotoxin-α (LTA), CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β, CCL7/MCP-3, CCL11/Eotaxin, CCL22/MDC, CXCL1/GROα, CXCL8/IL-8, CXCL9/MIG, CXCL10/IP-10, CX3CL1/Fractalkine, IL-1ra, IL-10, EGF, FGF-2/FGF-basic, Flt3 Ligand, G-CSF, M-CSF, GM-CSF, PDGF-AA, PDGF-AB/ BB, TGF-α, VEGF-A were measured via xMAP multiplexing technology. Significantly increased levels of 18 cytokines were found in blood plasma from COVID-19 patients during acute phase of the disease (as compared to control group), i.e., IL-6, IL-7, IL-15, IL-27, TNFα, TNFβ/Lymphotoxin-α (LTA), CCL2/MCP-1, CCL7/MCP-3, CXCL1/GROα, CXCL8/IL-8, CXCL10/IP-10, CXCL9/MIG, IL-1rа, IL-10, M-CSF, GM-CSF, VEGF-A. We found a significant decrease of nearly all the mentioned cytokines in recovered patients, in comparison with those who had moderate, severe/extremely severe disease. Moreover, we revealed a significantly decreased level of 8 cytokines in plasma from convalescents, as compared with control group, i.e., IL-1α, IL-2, IL-9, IL-12 p40, IL-18, CCL22/MDC, Flt3 Ligand, TGF-α. Immune response caused by SARS-CoV-2 infection involves multiple cytokines, mostly, with pro-inflammatory effects. We have shown for the first time that the convalescence phase is characterized by significantly lower levels of cytokines which regulate cellular differentiation and hematopoiesis (in particular, lymphocytes, T-cells and NK-cells). Over acute phase of the disease, the levels of these cytokines did not change. We revealed a significant decrease of most plasma cytokines upon recovery as compared to acute phase. On the contrary, acute phase of the disease is accompanied by significant increase of both pro- and antiinflammatory cytokines in blood plasma.

One-step quantitative RT-PCR assay with armored RNA controls for detection of SARS-CoV-2.

Coronavirus disease 2019 (COVID-19) has become pandemic since March 11, 2020. Thus, development and integration in clinics of fast and sensitive diagnostic tools are essential. The aim of the study is a development and evaluation of a one-step quantitative reverse transcription-polymerase chain reaction (RT-qPCR) assay (COVID-19 Amp) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection with an armored positive control and internal controls constructed from synthetic MS2-phage-based RNA particles. The COVID-19 Amp assay limit of detection was 103 copies/ml, the analytical specificity was 100%. A total of 109 biological samples were examined using COVID-19 Amp and World Health Organization (WHO)-based assay. Discordance in nine samples was observed (negative by the WHO-based assay) and discordant samples were retested as positive according to the results obtained from the Vector-PCRrv-2019-nCoV-RG assay. The developed COVID-19 Amp assay has high sensitivity and specificity, includes virus particles-based controls, provides the direct definition of the SARS-CoV-2 RdRp gene partial sequence, and is suitable for any hospital and laboratory equipped for RT-qPCR.