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.

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Modified synthesis of 3β-nicotinoyloxy-olean-12(13)-en-28-oic acid and 3-deoxy-3a-homo-3a-aza-28-hydroxy-olean-12(13)-ene from natural occurring oleanolic acid is suggested. These compounds and two others of ursane and lupane type triterpenoids (3-oximino-urs-12-en-28-oic acid and 3-deoxy-3a-homo-3a-aza-28-hydroxy-lup-12(13)-ene) were screened in vitro against Chlamydia trachomatis strain F-3271/Belarus/2015. Oleanane triterpenoids became the leading compounds with chemotherapeutic index > 8 and were chosen for further research.

Chlamydia trachomatis (CT) is a major cause of sexually transmitted diseases worldwide. The multilocus sequence typing (MLST) of clinical samples from random heterosexual chlamydia patients who were either asymptomatic or reported clinical manifestations of genital chlamydiosis (n = 63) in each of the seven major regions of the Republic of Belarus in 2017–2018 revealed 12 different CT sequence types (STs). We found seven known STs, ST4, ST6, ST9, ST13, ST38, ST95 and ST110, and five novel variants, namely ST271–ST275, which have not been detected elsewhere thus far. The ST4 variant was predominant (27/63, 42.9%) and detected in six out of seven regions. The two most common STs, ST9 and ST13, were regularly seen in four out of seven regions. In contrast, the remaining STs, ST6, ST38, ST95, ST110, and novel STs271-275, surfaced randomly in different parts of the country. The emergence of novel STs was registered in two regions, namely Minsk (ST271 and ST275) and Brest (ST271, ST272, ST273, and ST274). All the STs of detected CT strains were clustered into two Groups, I and III, which are characteristic of CT urogenital strains. No STs typical for Group II, specific to the LGV strains, were revealed. Our study contributes to better understanding the genetic diversity and molecular evolution of CT, one of the most important pathogens in public health worldwide.