The COVID-19 pandemic had a profound impact on influenza activity worldwide. However, as the pandemic progressed, influenza activity resumed. Here, we describe the influenza epidemic of high intensity of the 2022–2023 season. The epidemic had an early start and peaked in week 51.2022. The extremely high intensity of the epidemic may have been due to a significant decrease in herd immunity. The results of PCR-testing of 220,067 clinical samples revealed that the influenza A(H1N1)pdm09 virus dominated, causing 56.4% of positive cases, while A(H3N2) influenza subtype accounted for only 0.6%, and influenza B of Victoria lineage—for 34.3%. The influenza vaccine was found to be highly effective, with an estimated effectiveness of 92.7% in preventing admission with laboratory-confirmed influenza severe acute respiratory illness (SARI) cases and 54.7% in preventing influenza-like illness/acute respiratory illness (ILI/ARI) cases due to antigenic matching of circulated viruses with influenza vaccine strains for the season. Full genome next-generation sequencing of 1723 influenza A(H1N1)pdm09 viruses showed that all of them fell within clade 6B.1A.5.a2; nine of them possessed H275Y substitution in the NA gene, a genetic marker of oseltamivir resistance. Influenza A(H3N2) viruses belonged to subclade 3C.2a1b.2a.2 with the genetic group 2b being dominant. All 433 influenza B viruses belonged to subclade V1A.3a.2 encoding HA1 substitutions A127T, P144L, and K203R, which could be further divided into two subgroups. None of the influenza A(H3N2) and B viruses sequenced had markers of resistance to NA inhibitors. Thus, despite the continuing circulation of Omicron descendant lineages, influenza activity has resumed in full force, raising concerns about the intensity of fore coming seasonal epidemics.

Human seasonal coronaviruses (hCoVs) are a group of viruses that affect the upper respiratory tract. While seasonal patterns and the annual variability of predominant hCoV species are well-documented, their genetic and species diversity in St. Petersburg and across Russia remains largely unexplored. In this study, we developed a two-pool, long-amplicon (900–1100 bp) PCR primer panel for the whole-genome sequencing of four seasonal hCoV species. The panel was validated using nasopharyngeal swab samples collected within the Global Influenza Hospital Surveillance Network (GIHSN) project. Over a period of six epidemiological seasons from 2017 to 2023, we retrospectively analyzed 14,704 nasopharyngeal swabs collected from patients hospitalized in St. Petersburg clinics. Of these samples, 5010 (34.07%) tested positive for respiratory viruses, with 424 (2.88% of all samples) identified as seasonal human coronaviruses. The assessment of species diversity showed that predominant hCoV species alternate between seasons. Whole-genome sequences for 85 seasonal human coronaviruses (hCoVs) with >70% genome coverage were obtained, including 23 hCoV-OC43, 6 hCoV-HKU1, 39 hCoV-229E, and 17 hCoV-NL63. These represent the first near-complete genomes of seasonal hCoVs from the Russian Federation, addressing a significant gap in the genomic epidemiology of these viruses. A detailed phylogenetic analysis of the sequenced genomes was conducted, highlighting the emergence of hCoV-229E subclades 7b.1 and 7b.2, which carry numerous substitutions in the Spike protein. Additionally, we sequenced a historical hCoV-229E isolate collected in the USSR in 1979, the oldest sequenced 229E virus from Eurasia, and demonstrated that it belongs to Genotype 2. The newly developed PCR-based sequencing protocol for seasonal hCoVs is straightforward and well-suited for genomic surveillance, providing a valuable tool to enhance our understanding of the genetic diversity of human seasonal coronaviruses.

Objective: to analyze the epidemiological and clinical features of acute respiratory infections occurring during the St. Petersburg 2017–2018 and 2018–2019 epidemic seasons.Materials and methods: the study included 457 patients, treated in St. Petersburg clinics from 2017–2019, displaying symptoms of acute respiratory infection (ARI), including evaluation of their clinical histories. Pathogen types were determined by polymerase chain reaction (PCR). Data analysis was carried out using mathematical statistics methods using the Statistica 10 software package (StatSoft Inc.).Results: in this study, we examined the epidemiological and clinical features of acute respiratory infections in St. Petersburg occurring during two epidemic seasons, 2017–2018 and 2018–2019. The 2017–2018 season was characterized by a prevalence of infections caused by influenza B viruses and influenza A subtype H3N2 viruses. In the 2018–2019 season, there was a greater number of acute respiratory viral infections (ARVIs) and infections caused by influenza A subtype H1N1pdm; influenza B virus was detected only in isolated cases. In the 2017–2018 sore throats and muscle aches were a characteristic symptom of influenza A H1N1pdm infections, of bacterial infections – only sore throats. It was shown that throat pain and vasodilation of the scleral and soft palate vessels were significantly more frequent in the 2017–2018 season, compared to the 2018–2019 season. Cough and redness of the posterior pharyngeal wall were hallmark signs of ARVIs in the 2018–2019 season.Conclusion: according to the data, each epidemic season is characterized not only by its own type-specific acute respiratory infection frequencies, but also by different clinical manifestation frequencies. For global monitoring, treatment effectiveness evaluation, and refined study of acute respiratory infection clinical features, it is advisable to use approaches which incorporate accurate, specific, and rapid molecular biological methods capable of identifying a broad range of pathogens.

BACKGROUND: Respiratory viruses circulate everywhere. Problem of pandemic respiratory virus SARS-CoV-2 is especially relevant. The understanding of level of circulation of different viruses can help in developing a strategy of respiratory viruses combat. AIM: To compare circulation of respiratory viruses during different seasons. MATERIALS AND METHODS: PCR-diagnostic. RESULTS: The most common viruses before the pandemic were influenza and respiratory syncytial viruses. COVID-19 pandemic season 2020/2021 had significant difference from previous epidemic seasons. Influenza viruses have largely disappeared, but the circulation of seasonal coronavirus and metapneumovirus has increased. The circulation of rhinovirus remained at the same level. CONCLUSIONS: The emergence of pandemic SARS-CoV-2 virus had a significant impact on some respiratory viruses circulation, such as influenza or respiratory syncytial viruses.

Objective. To analyze the age-related characteristics of the contribution of influenza viruses, RSV, SARS-CoV-2, other pathogens to the development of severe acute respiratory infections (SARI) in children with an assessment of the disease severity depending on its etiology and epidemic period. Materials and methods. SARI monitoring was carried out over six consecutive epidemic seasons, starting from 2018–2019 in 9 infectious hospitals of three cities of Russia with an assessment of the disease severity depending on its etiology. Results. Among all hospitalized children, the proportion of children hospitalized with laboratory-confirmed influenza from 2018 to 2020 ranged from 25.7% to 44.7%, and for RSV infection from 25.7% to 26.8%. However, during the peak of the pandemic, these rates dropped significantly to 0.3% and 1.7%, respectively. In the subsequent three seasons (2021–2024), laboratory-confirmed influenza among hospitalized children was registered in 4.5–20.2% of cases, while RSV infection was identified in 13.4–24.1% of cases, accompanied by a shift in viral subgroups. RSV infections were most severe during the 2022–2023 season, presenting in some cases with hyperthermia, hypoxia, dyspnea, and altered consciousness. Among hospitalized children, the proportion with COVID-19 was relatively low in 2020–2021 (0.8–2.4%) but increased significantly to 10.6%–13.6% following the emergence of the Omicron variant in 2022, before decreasing again in subsequent years. The main genetic lineages of SARS-CoV-2 circulating in the Russian Federation are presented. Conclusion. Influenza and RSV viruses were predominant among viral pathogens identified in hospitalized children aged ≤ 2 years. COVID-19 cases among children were relatively rare and generally less severe compared to RSV and rhinovirus infections.