ABSTRACT
Objective: To study the seroprevalence of SARS-CoV-2 antibodies (AB) in children in the 2nd year of the COVID-19 pandemic in Russia. Materials and methods: Prospective cohort study. The seroprevalence research was conducted among 3670 children aged 1 to 17 y/o from 26 modelling regions of Russia (that have been participating earlier in the five stages of seromonitoring during 2020-2021). The serological testing was carried out in December, 2021. The work was carried out according to a unified methodology set by the Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being with the Pasteur Institute of Epidemiology and Microbiology (Saint Petersburg, Russia). The plasma was obtained from 3 ml of venous blood, in which the level of AB to nucleocapsid (NC), and the SARS-CoV-2 receptor-binding domain (RBD) was determined by immunoferment method using reagents for qualitative and quantitative analysis. Results: The analysis of AB seroprevalence to NC and RBD showed the statistically significant increase in the share of seropositivity to RBD in children of all modelling regions (p<0.05). The most seropositive volunteers contained low levels of AB: 31.3-125.6 BAU/ml NC and 22.6-220 BAU/ml RBD. An increase in the level of AB to NC and RBD was accompanied by a decrease in the percentage of seropositive patients. Evaluating the contribution of children to the level of humoral immunity, convalescents (had been ill shortly before the examination), the «anamnesis» (had been ill at previous stages of seromonitoring) and asymptomatic (had been asymptomatically ill) groups were distinguished. The maximum contribution was made by children with asymptomatic cases of COVID-19 in anamnesis: In 82.3% (95% CI 81.1-83.6), of which 76.9% (95% CI 75.5-78.3) AB detected to RBD. The contribution of children of two other groups to the overall level of humoral immunity was 33 times less. Conclusion: Statistically significant predominance of AB to RBD above AB to NC and their main contribution to the level of humoral immunity to SARS-CоV-2 (p<0.001).
ABSTRACT
The main histocompatibility complex – HLA system (Human Leukocyte Antigens) is among the most important genetic factors determining response of humans to infectious agents. The key role that HLA molecules play in immune response is to present the pathogen-derived peptides. Enormous molecular variability of HLA alleles in human populations have attracted close attention and became the basis for numerous studies aimed at evaluating the role of HLA genotypes for individual features of immune response to COVID-19, the new infection caused by SARS-CoV-2 β-coronavirus. Many studies have focused on search of specific alleles associated with both susceptibility and resistance to this disease. Separate HLA patterns were reported already. These patterns may be either universal to several populations, or rather peculiar, since distribution of HLA genes is different for various populations, depending on the living conditions, including specific protection from environmental pathogens. Therefore, it is evident that individual effects of HLA genotype upon occurrence and course of SARS-CoV-2 infection should be performed in comparison with the HLA distribution among the residents of appropriate region. The objective of this study was to compare the distribution of HLA-A*, B*, DRB1* allele groups, and to analyze the frequencies of HLA-AB-DRB1 haplotypes in subjects with COVID-19 (n = 138), compared with the control group presented by residents of the North-Western Russia (n = 1456). The most significant differences between COVID-19 patients compared with a group from control population were revealed for the groups of HLA-A* alleles: the frequencies of HLA-A*02 and HLA-A*26 were significantly reduced (39.86% versus 51.72%, χ2 = 7,58, and 4.35% versus 9.07%, χ2 = 4.17, respectively). At the same time, the frequency of HLA-A*29 was increased more than 2-fold (5.80% versus 2.47%, χ2 = 4.03). This finding suggests that the allele groups A*02 and A*26 are associated with reduced likelihood of the disease, while A*29, is an apparent factor predisposing for susceptibility to the disease. It was found that occurrence of definite HLA haplotypes, including the A*02 allele group, is less common in persons who have undergone COVID-19, and are ranged at the 4th, 7th and 10th positions in frequency, while in the population control group such HLA haplotypes took the 3rd, 4th, 7th and 8th places. Further evaluation of the HLA gene polymorphism will allow to understand the predetermined immunogenetic basis for susceptibility, as well as clinical severity of COVID-19.
ABSTRACT
The novel coronavirus (SARS-CoV-2) pandemic, dubbed COVID-19, has become one of the most serious challenges for human populations in the vast majority of countries worldwide. Rapid spreading and increased mortality related to it required new approaches to manage epidemic processes on a global scale. One of such approaches was based on analyzing SARS-CoV-2 seroprevalence associated with COVID-19. Our aim was to summarize the results on assessing seroprevalence to the SARS-CoV-2 nucleocapsid antigen (Nc) in residents from 26 regions of the Russian Federation, carried out during the first wave of the COVID-19 epidemic. Materials and methods. Seroprevalence distribution was examined in 26 model regions of the Russian Federation according to the unified method developed by the Rospotrebnadzor with the participation of the Federal State Institution Saint Petersburg Pasteur Research Institute of Epidemiology and Microbiology. Such approach implied formation of a group of volunteer subjects in model geographic region who were tested by ELISA for anti-Nc serum antibody level in peripheral blood. Analyzed primary data obtained in separate regions were either accepted for publication or released. Results. The current paper finalizes the data obtained in all 26 regions of the Russian Federation. The total SARS-CoV-2 seroprevalence was 19.5 (10.0-25.6)% with the maximum and minimum value found in the Kaliningrad Region and the Republic of Crimea, respectively (50.2% vs. 4.3%). A pattern of age-related seroprevalence distribution indicates insignificant predominance of seroprevalence among subjects of 1-17 years old: 22.1 (13.1-31.8)%. Among COVID-19 convalescents positive for SARS-CoV Nc antibodies it reached 60.0 (40.0-73.3)%. The number of contact persons comprised 6285 subjects or 8.5% of total volunteer cohort, with the level of seroprevalence reaching up to 25.3 (17.95-35.8)%. A direct correlation was revealed between levels of seroprevalence in convalescent and contact volunteers. In addition, the reproductive number for SARS-CoV was calculated comprising 5.8 (4.3-8.5) suggesting that one convalescent subject can infect at least 4 healthy individuals. A high level of asymptomatic forms of COVID-19 among seropositive subjects was confirmed empirically comprising up to 93.6 (87.1-94.9)%. Conclusion. A single cross-sectional study performed during 2020 June-August timeframe allowed to assess pattern of sex- and age-related COVID-19 seroprevalence for general population in 26 Russian Federation regions. The data obtained may serve as a basis for the longitudinal cohort investigation with serial subject sampling. The timing and duration of study will be determined by dynamics of ongoing COVID-19 epidemic.
ABSTRACT
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. © 2020 Russian Research Anti-Plague Institute. All rights reserved.