SARS-CoV-2 collective immunity among the population of the Republic of Armenia

Background. The COVID-19 pandemic has become a substantial global health crisis, unparalleled in world history. Infection dynamics can have specific characteristics in different countries due to social, economic, climatic, or geographic factors. Aim: to study features of SARS-CoV-2 collective immunity among the Armenian population. Materials and methods. A cross-sectional, randomized study of collective immunity was carried out according to a program developed by Rospotrebnadzor and the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The study was approved by the ethics committees of the National Center for Infectious Diseases (Armenia) and the St. Petersburg Pasteur Institute (Russia). A volunteer cohort was formed (N = 6057), randomized by age and region. The studys analysis included: shares and distributions of antibodies (Abs) to nucleocapsid (Nc) antigen (Ag) and receptor binding domain (RBD) S-1 Ag in the cohort; and quantitative determination of these Abs by ELISA. During the survey, a history of vaccination was indicated by 4395 people. Results. Overall seropositivity formed in the whole cohort (by April 14, 2022) was 98.6% (95% CI: 98.198.7). It did not depend on age, place of residence, or occupation. When quantifying Nc and RBD Abs, the proportions of volunteers with Nc Ab levels of 117 BAU/ml and RBD Ab levels of 22.6220 BAU/ml were the smallest, amounting to 6.9% (95% CI: 6.27.5) and 20.4% (95% CI: 19.421.4), respectively. With increasing serum concentrations (Nc 667 BAU/ml, RBD 450 BAU/ml), the proportions of individuals with the corresponding levels were 20.2% for Nc (95% CI: 19.221.3) and 54.2% for RBD (95% CI: 52.955.5). Vaccination coverage was 72.6% (95% CI: 71.573.7). The most frequently used were Sinopharm/BIBP (32.4%), AZD1222 (22.3%), and Gam-COVID-Vac (21%). The remaining vaccines (CoronaVac, mRNA-1273, BNT162b2, CoviVac) were used by 24.3% of vaccinated individuals. When summing vaccines by platform, it was found that: vector vaccines were used in 40.34% (95% CI: 33.5742.39) of cases; whole-virion vaccines were used in 26.83% (95% CI: 24.7632.20); and mRNA vaccines were used in 6.33% (95% CI: 4.848.91). Conclusion. The epidemic situation in Armenia by April 2022 was characterized by a high level of collective immunity, independent of age or regional factors. Vector and whole-virion vaccines have been used most widely.