Characteristics of the COVID-19 epidemic process in the Northwestern Federal District during the circulation period of the Omicron variant (2022–2024)

Abstract

Introduction. COVID-19, caused by SARS-CoV-2, remains a significant global health issue. Since late 2021, the Omicron variant has become dominant, characterized by high transmissibility but reduced virulence. Studying the regional characteristics of the epidemic process during its circulation is essential for assessing the transformation of the COVID-19 epidemic process and the emergence of circulation patterns approaching endemicity. Objective. Analysis of the epidemiological situation of COVID-19 in the Northwestern Federal District of the Russian Federation during the period of dominance of the SARS-CoV-2 Omicron variant. Materials and methods. An analysis of Rospotrebnadzor statistical data on morbidity, case fatality rate, age structure, and severity of COVID-19 in the Northwestern Federal District (NWFD) for 2022–2024 was conducted. To study genetic diversity, S-gene sequencing was performed on 16,008 samples from COVID-19 patients across 11 subjects of the Northwestern Federal District to determine the genetic lineages of circulating strains. Results. A decrease in annual morbidity was observed, from 1,768,558 cases in 2022 to 145,482 in 2024. Morbidity exhibited a wave-like pattern with peaks associated with the succession of Omicron subvariants. A shift in morbidity towards the 65+ age group was noted (an increase in proportion from 12.0% to 22.7%). The proportion of severe forms has decreased significantly (from 3.7% to 0.2%), and case fatality rate decreased from 4.4% to 0.2%, while the proportion of mild and asymptomatic cases increased. Conclusion. The data suggest the emergence of features of SARS-CoV-2 circulation in the NWFD approaching an endemic pattern, accompanied by a decrease in severe cases and case fatality rate amid the continued replacement of Omicron subvariants. At the same time, the decline in reported morbidity should be interpreted with caution because it may have been affected by changes in testing coverage, case ascertainment, and registration practices. The results confirm the need to maintain molecular epidemiological surveillance; expanded genomic monitoring, including whole-genome sequencing, is required for the detection and detailed characterization of new potentially significant variants.