{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T01:04:27Z","timestamp":1760058267408,"version":"build-2065373602"},"reference-count":42,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2025,3,27]],"date-time":"2025-03-27T00:00:00Z","timestamp":1743033600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Ministry of Science and Higher Education","award":["FGWG-2023-0002"],"award-info":[{"award-number":["FGWG-2023-0002"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Viruses"],"abstract":"<jats:p>Introduction: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) underwent significant mutations, resulting in the Omicron variant. Methods: In this study, we analyzed blood samples from 98 patients with acute coronavirus disease 19 (COVID-19) hospitalized during the initial SARS-CoV-2 wave and the onset of Omicron in 2021. High-resolution melting (HRM) analysis of PCR products was used to analyze RNA extracted from clinical samples collected in July and November 2021 from patients infected with SARS-CoV-2. Results: HRM analysis revealed a characteristic deletion in the N protein RNA of the virus isolated in November 2021, associated with the Omicron variant. Elevated levels of inflammatory markers and interleukin-6 (IL-6) were observed in both waves of COVID-19. Complement levels and IgG and IgM antibodies to SARS-CoV-2 were detected more often during the second wave. An increase in hemagglutinin-inhibiting (HI) antibodies against influenza viruses was observed in paired blood specimens from moderate to severe COVID-19 patients during both outbreaks. Conclusions: Patients admitted during both waves of COVID-19 showed a significant rise in inflammatory markers, suggesting that Omicron triggers inflammatory responses. The rapid formation of IgM and IgG in Omicron may indicate a faster immune response. Seasonal flu may negatively impact the clinical course of coronavirus infections.<\/jats:p>","DOI":"10.3390\/v17040481","type":"journal-article","created":{"date-parts":[[2025,3,28]],"date-time":"2025-03-28T06:06:35Z","timestamp":1743141995000},"page":"481","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["The Clinical and Laboratory Landscape of COVID-19 During the Initial Period of the Pandemic and at the Beginning of the Omicron Era"],"prefix":"10.3390","volume":"17","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9794-3520","authenticated-orcid":false,"given":"Yulia A.","family":"Desheva","sequence":"first","affiliation":[{"name":"Federal State Budgetary Scientific Institution \u2018Institute of Experimental Medicine\u2019, 12, Acad. Pavlov Street, 197022 Saint-Petersburg, Russia"},{"name":"Medical Institute, St Petersburg University, 21st Line, bldg. 8a, 199034 Saint-Petersburg, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6649-8150","authenticated-orcid":false,"given":"Tamara N.","family":"Shvedova","sequence":"additional","affiliation":[{"name":"Vsevolozhsk Clinical Interdistrict Hospital, 20, Koltushskoe Highway, Leningrad Region, 188643 Arkhangelsk, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Olga S.","family":"Kopteva","sequence":"additional","affiliation":[{"name":"Federal State Budgetary Scientific Institution \u2018Institute of Experimental Medicine\u2019, 12, Acad. Pavlov Street, 197022 Saint-Petersburg, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-1680-399X","authenticated-orcid":false,"given":"Danila S.","family":"Guzenkov","sequence":"additional","affiliation":[{"name":"Federal State Budgetary Scientific Institution \u2018Institute of Experimental Medicine\u2019, 12, Acad. Pavlov Street, 197022 Saint-Petersburg, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3342-5828","authenticated-orcid":false,"given":"Polina A.","family":"Kudar","sequence":"additional","affiliation":[{"name":"Federal State Budgetary Scientific Institution \u2018Institute of Experimental Medicine\u2019, 12, Acad. Pavlov Street, 197022 Saint-Petersburg, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tatiana S.","family":"Kotomina","sequence":"additional","affiliation":[{"name":"Federal State Budgetary Scientific Institution \u2018Institute of Experimental Medicine\u2019, 12, Acad. Pavlov Street, 197022 Saint-Petersburg, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-0045-4886","authenticated-orcid":false,"given":"Daria S.","family":"Petrachkova","sequence":"additional","affiliation":[{"name":"Federal State Budgetary Scientific Institution \u2018Institute of Experimental Medicine\u2019, 12, Acad. Pavlov Street, 197022 Saint-Petersburg, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8439-6502","authenticated-orcid":false,"given":"Elena P.","family":"Grigorieva","sequence":"additional","affiliation":[{"name":"Federal State Budgetary Scientific Institution \u2018Institute of Experimental Medicine\u2019, 12, Acad. Pavlov Street, 197022 Saint-Petersburg, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Anna A.","family":"Lerner","sequence":"additional","affiliation":[{"name":"Department of Clinical Laboratory Diagnostics, Biological and General Chemistry, Federal State Budgetary Educational Institution of Higher Education North-West State Medical University, 191015 Saint-Petersburg, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Stanislav V.","family":"Ponkratov","sequence":"additional","affiliation":[{"name":"Vsevolozhsk Clinical Interdistrict Hospital, 20, Koltushskoe Highway, Leningrad Region, 188643 Arkhangelsk, Russia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,3,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"5595","DOI":"10.2147\/IDR.S492816","article-title":"Changes in Clinical Features and Severity of COVID-19 with the Emergence of Omicron Variants: A Shift Towards a Common Disease","volume":"17","author":"Kawamura","year":"2024","journal-title":"Infect. 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