{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T16:51:49Z","timestamp":1791305509995,"version":"4.3.1"},"reference-count":34,"publisher":"Ovid Technologies (Wolters Kluwer Health)","issue":"10","content-domain":{"domain":["lww.com","ovid.com"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,10]]},"abstract":"<jats:sec>\n                    <jats:title>OBJECTIVES:<\/jats:title>\n                    <jats:p>Since the onset of the COVID-19-pandemic, emerging virus variants, increasing population immunity, and evolving treatment strategies have substantially altered disease severity. This study aimed to identify predictors of critical illness due to COVID-19 over time and compare them with those of seasonal influenza in Sweden.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>DESIGN, SETTING, PATIENTS, AND MEASUREMENTS:<\/jats:title>\n                    <jats:p>We conducted a retrospective, population-based cohort study using nationwide registry data. All individuals hospitalized for COVID-19 between 2020 and 2022 were categorized into five groups, based on pandemic waves and dominating virus variants. A sixth group included all patients hospitalized for influenza between 2018 and 2022. Patients were followed from hospitalization until ICU admission, in-hospital death, discharge, or end of study. Incidence rates were calculated and Cox regression identified predictors of ICU admission and in-hospital mortality, adjusting for age, sex, socioeconomic factors, comorbidities, and severe acute respiratory syndrome corona virus 2-vaccination. Data on influenza vaccinations were not available from the registers.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>MAIN RESULTS:<\/jats:title>\n                    <jats:p>We included 92,428 COVID-19 hospitalizations and 21,355 influenza hospitalizations. Hospitalization rates were lowest during the delta-dominant period, while ICU admission rates were lowest during the Omicron-dominant period. The Omicron period most closely resembled influenza inpatient demographics, hospital stay duration, ICU admissions, and in-hospital mortality. Age distributions varied across pandemic periods, with the Omicron period showing an age profile similar to influenza (\u2248 50% \u2265 75 yr). Adjusted hazard ratios for ICU-admission were strongest in unvaccinated patients, males, and individuals of 45\u201374 years for COVID-19, and in individuals of 45\u201364 years or with chronic lung diseases for influenza. Common predictors of in-hospital mortality included age older than 45 years (with a sharp increase after 74), male sex, and chronic comorbidities, and for COVID-19 also unvaccinated status.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>CONCLUSIONS:<\/jats:title>\n                    <jats:p>Although COVID-19 consistently resulted in higher hospitalization rates than influenza, demographic and clinical patterns converged during the later pandemic stages. Advanced age was the strongest predictor of severe illness in both infections, with lack of vaccination additionally associated with severe COVID-19.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1097\/ccm.0000000000007308","type":"journal-article","created":{"date-parts":[[2026,9,7]],"date-time":"2026-09-07T14:00:14Z","timestamp":1788789614000},"page":"2670-2685","update-policy":"https:\/\/doi.org\/10.1097\/lww.0000000000001000","source":"Crossref","is-referenced-by-count":0,"title":["Predictors of Critical Illness During Different COVID-19 Pandemic Periods Compared With Seasonal Influenza"],"prefix":"10.1097","volume":"54","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2400-4092","authenticated-orcid":false,"given":"Josefine","family":"Beck-Friis","sequence":"first","affiliation":[{"name":"Department of Infectious Diseases, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden."},{"name":"Department of Infectious Diseases, Region V\u00e4stra G\u00f6taland, Sahlgrenska University Hospital, Gothenburg, Sweden."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ailiana","family":"Santosa","sequence":"additional","affiliation":[{"name":"School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Huiqi","family":"Li","sequence":"additional","affiliation":[{"name":"School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Fredrik","family":"Nyberg","sequence":"additional","affiliation":[{"name":"School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Magnus","family":"Gissl\u00e9n","sequence":"additional","affiliation":[{"name":"Department of Infectious Diseases, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden."},{"name":"Department of Infectious Diseases, Region V\u00e4stra G\u00f6taland, Sahlgrenska University Hospital, Gothenburg, Sweden."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jonatan","family":"Oras","sequence":"additional","affiliation":[{"name":"Department of Anesthesiology and Intensive Care Medicine, Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden."},{"name":"Department of Anesthesia and Intensive Care, Region V\u00e4stra G\u00f6taland, Sahlgrenska University Hospital, Gothenburg, Sweden."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aylin","family":"Yilmaz","sequence":"additional","affiliation":[{"name":"Department of Infectious Diseases, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden."},{"name":"Department of Infectious Diseases, Region V\u00e4stra G\u00f6taland, Sahlgrenska University Hospital, Gothenburg, Sweden."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"276","published-online":{"date-parts":[[2026,9,7]]},"reference":[{"key":"R5-20261006","first-page":"162","article-title":"SARS-CoV-2 variant biology: Immune escape, transmission and fitness.","volume":"21","author":"Carabelli","year":"2023","journal-title":"Nat Rev Microbiol"},{"key":"R6-20261006","doi-asserted-by":"crossref","first-page":"547","DOI":"10.1093\/cid\/ciad276","article-title":"Changing severity and epidemiology of adults hospitalized with coronavirus disease 2019 (COVID-19) in the United States after introduction of COVID-19 vaccines, March 2021-August 2022.","volume":"77","author":"Kojima","year":"2023","journal-title":"Clin Infect Dis"},{"key":"R7-20261006","doi-asserted-by":"crossref","first-page":"427","DOI":"10.1186\/s13054-023-04722-0","article-title":"Clinical outcomes during and beyond different COVID-19 critical illness variant periods compared with other lower respiratory tract infections.","volume":"27","author":"Hedberg","year":"2023","journal-title":"Crit Care"},{"key":"R8-20261006","doi-asserted-by":"crossref","first-page":"104799","DOI":"10.1016\/j.ebiom.2023.104799","article-title":"Risk of COVID-19 after natural infection or vaccination.","volume":"96","author":"Rick","year":"2023","journal-title":"EBioMedicine"},{"key":"R9-20261006","first-page":"1267","article-title":"From alpha to Omicron: How different variants of concern of the SARS-Coronavirus-2 impacted the world.","volume":"12","author":"Andre","year":"2023","journal-title":"Biology (Basel)"},{"key":"R10-20261006","doi-asserted-by":"crossref","first-page":"697","DOI":"10.1016\/S0140-6736(17)30129-0","article-title":"Influenza.","volume":"390","author":"Paules","year":"2017","journal-title":"Lancet"},{"key":"R11-20261006","doi-asserted-by":"crossref","first-page":"649","DOI":"10.2147\/CLEP.S312742","article-title":"Swedish Covid-19 investigation for future insights \u2013 A population epidemiology approach using register linkage (SCIFI-PEARL).","volume":"13","author":"Nyberg","year":"2021","journal-title":"Clin Epidemiol"},{"key":"R13-20261006","doi-asserted-by":"crossref","first-page":"ofad244","DOI":"10.1093\/ofid\/ofad244","article-title":"Age differences in comorbidities, presenting symptoms, and outcomes of influenza illness requiring hospitalization: A worldwide perspective from the global influenza hospital surveillance network.","volume":"10","author":"Andrew","year":"2023","journal-title":"Open Forum Infect Dis"},{"key":"R14-20261006","doi-asserted-by":"crossref","first-page":"e0286142","DOI":"10.1371\/journal.pone.0286142","article-title":"COVID-19 hospitalisations and all-cause mortality by risk group in Finland.","volume":"18","author":"Summanen","year":"2023","journal-title":"PLoS One"},{"key":"R15-20261006","doi-asserted-by":"crossref","first-page":"e206","DOI":"10.1093\/cid\/ciaa1012","article-title":"Risk factors for intensive care unit admission and in-hospital mortality among hospitalized adults identified through the US coronavirus disease 2019 (COVID-19)-Associated hospitalization surveillance network (COVID-NET).","volume":"72","author":"Kim","year":"2021","journal-title":"Clin Infect Dis"},{"key":"R16-20261006","doi-asserted-by":"crossref","first-page":"165","DOI":"10.1038\/s41590-021-01091-0","article-title":"Innate immunity: The first line of defense against SARS-CoV-2.","volume":"23","author":"Diamond","year":"2022","journal-title":"Nat Immunol"},{"key":"R17-20261006","doi-asserted-by":"crossref","first-page":"748591","DOI":"10.3389\/fragi.2021.748591","article-title":"Patho-physiology of aging and immune-senescence: Possible correlates with comorbidity and mortality in middle-aged and old COVID-19 patients.","volume":"2","author":"Farheen","year":"2021","journal-title":"Front Aging"},{"key":"R18-20261006","doi-asserted-by":"crossref","first-page":"369","DOI":"10.1089\/jir.2022.0029","article-title":"Comparing the cytokine storms of COVID-19 and pandemic influenza.","volume":"42","author":"Pacheco-Hernandez","year":"2022","journal-title":"J Interferon Cytokine Res"},{"key":"R19-20261006","doi-asserted-by":"crossref","first-page":"2466699","DOI":"10.1080\/22221751.2025.2466699","article-title":"Vaccine effectiveness dynamics against influenza and SARS-CoV-2 in community-tested patients in France 2023-2024.","volume":"14","author":"Abou Chakra","year":"2025","journal-title":"Emerg Microbes Infect"},{"key":"R20-20261006","doi-asserted-by":"crossref","first-page":"714","DOI":"10.1016\/S2213-2600(24)00179-6","article-title":"Estimated number of lives directly saved by COVID-19 vaccination programmes in the WHO European Region from December, 2020, to March, 2023: A retrospective surveillance study.","volume":"12","author":"Mesl\u00e9","year":"2024","journal-title":"Lancet Respir Med"},{"key":"R21-20261006","doi-asserted-by":"crossref","first-page":"127690","DOI":"10.1016\/j.vaccine.2025.127690","article-title":"Assessment of influenza vaccine effectiveness among the elderly in Taiwan using population-based registry data for the 2023-2024 season.","volume":"64","author":"Huang","year":"2025","journal-title":"Vaccine"},{"key":"R22-20261006","doi-asserted-by":"crossref","first-page":"6640","DOI":"10.1016\/j.vaccine.2022.09.065","article-title":"An intersectional analysis of sociodemographic disparities in Covid-19 vaccination: A nationwide register-based study in Sweden.","volume":"40","author":"Spetz","year":"2022","journal-title":"Vaccine"},{"key":"R23-20261006","doi-asserted-by":"crossref","first-page":"2400076","DOI":"10.2807\/1560-7917.ES.2024.29.7.2400076","article-title":"2023\/24 mid-season influenza and Omicron XBB.1.5 vaccine effectiveness estimates from the Canadian Sentinel Practitioner Surveillance Network (SPSN).","volume":"29","author":"Skowronski","year":"2024","journal-title":"Euro Surveill"},{"key":"R24-20261006","doi-asserted-by":"crossref","first-page":"715","DOI":"10.1038\/s41586-022-04479-6","article-title":"SARS-CoV-2 Omicron variant replication in human bronchus and lung ex vivo.","volume":"603","author":"Hui","year":"2022","journal-title":"Nature"},{"key":"R25-20261006","doi-asserted-by":"crossref","first-page":"1113793","DOI":"10.3389\/fpubh.2023.1113793","article-title":"Predisposing factors for admission to intensive care units of patients with COVID-19 infection \u2013 Results of the German nationwide inpatient sample.","volume":"11","author":"Keller","year":"2023","journal-title":"Front Public Health"},{"key":"R26-20261006","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.jhin.2023.04.014","article-title":"Outcomes of influenza and COVID-19 inpatients in different phases of the SARS-CoV-2 pandemic: A single-centre retrospective case-control study.","volume":"138","author":"Bechmann","year":"2023","journal-title":"J Hosp Infect"},{"key":"R27-20261006","doi-asserted-by":"crossref","first-page":"29","DOI":"10.1186\/s13293-020-00304-9","article-title":"Impact of sex and gender on COVID-19 outcomes in Europe.","volume":"11","author":"Gebhard","year":"2020","journal-title":"Biol Sex Differ"},{"key":"R28-20261006","doi-asserted-by":"crossref","first-page":"429","DOI":"10.1111\/imm.13487","article-title":"The immune response to COVID-19: Does sex matter?","volume":"166","author":"Ho","year":"2022","journal-title":"Immunology"},{"key":"R29-20261006","doi-asserted-by":"crossref","DOI":"10.3390\/ijms21165793","article-title":"Obesity and COVID-19: Molecular mechanisms linking both pandemics.","volume":"21","author":"Ritter","year":"2020","journal-title":"Int J Mol Sci"},{"key":"R30-20261006","doi-asserted-by":"crossref","first-page":"484","DOI":"10.1097\/CCM.0000000000005788","article-title":"Age moderates the effect of obesity on mortality risk in critically ill patients with COVID-19: A nationwide observational cohort study.","volume":"51","author":"den Uil","year":"2023","journal-title":"Crit Care Med"},{"key":"R31-20261006","doi-asserted-by":"crossref","first-page":"3844","DOI":"10.3390\/jcm11133844","article-title":"Obesity impact on SARS-CoV-2 infection: Pros and Cons \u201cObesity Paradox\u201d \u2013 A systematic review.","volume":"11","author":"Vulturar","year":"2022","journal-title":"J Clin Med"},{"key":"R32-20261006","first-page":"CD015201","article-title":"Obesity as an independent risk factor for COVID-19 severity and mortality.","volume":"5","author":"Tadayon Najafabadi","year":"2023","journal-title":"Cochrane Database Syst Rev"},{"key":"R34-20261006","doi-asserted-by":"crossref","first-page":"255","DOI":"10.1038\/nrneph.2013.44","article-title":"Immune cell dysfunction and inflammation in end-stage renal disease.","volume":"9","author":"Betjes","year":"2013","journal-title":"Nat Rev Nephrol"},{"key":"R35-20261006","doi-asserted-by":"crossref","first-page":"84","DOI":"10.18433\/jpps31455","article-title":"Epithelial and endothelial expressions of ACE2: SARS-CoV-2 entry routes.","volume":"24","author":"Guney","year":"2021","journal-title":"J Pharm Pharm Sci"},{"key":"R36-20261006","doi-asserted-by":"crossref","first-page":"12906","DOI":"10.3390\/ijms232112906","article-title":"The role of inflammation in cardiovascular disease.","volume":"23","author":"Henein","year":"2022","journal-title":"Int J Mol Sci"},{"key":"R37-20261006","doi-asserted-by":"crossref","first-page":"1147","DOI":"10.1038\/s41440-022-00922-3","article-title":"Impact of renin-angiotensin-aldosterone system inhibitors on COVID-19.","volume":"45","author":"Matsuzawa","year":"2022","journal-title":"Hypertens Res"},{"key":"R38-20261006","doi-asserted-by":"crossref","first-page":"1183","DOI":"10.1001\/jama.2023.4480","article-title":"Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19: A randomized clinical trial.","volume":"329","author":"Lawler","year":"2023","journal-title":"JAMA"},{"key":"R39-20261006","doi-asserted-by":"crossref","first-page":"574","DOI":"10.1093\/eurpub\/ckad094","article-title":"Waves of inequality: Income differences in intensive care due to COVID-19 in Sweden.","volume":"33","author":"Gauffin","year":"2023","journal-title":"Eur J Public Health"},{"key":"R40-20261006","doi-asserted-by":"crossref","first-page":"100095","DOI":"10.1016\/j.gloepi.2022.100095","article-title":"COVID-19 in people aged 18-64 in Sweden in the first year of the pandemic: Key factors for severe disease and death.","volume":"4","author":"Rosengren","year":"2022","journal-title":"Glob Epidemiol"}],"container-title":["Critical Care Medicine"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.ovid.com\/10.1097\/CCM.0000000000007308","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T16:01:19Z","timestamp":1791302479000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.ovid.com\/10.1097\/CCM.0000000000007308"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,7]]},"references-count":34,"journal-issue":{"issue":"10","published-print":{"date-parts":[[2026]]}},"URL":"https:\/\/doi.org\/10.1097\/ccm.0000000000007308","relation":{},"ISSN":["0090-3493","1530-0293"],"issn-type":[{"value":"0090-3493","type":"print"},{"value":"1530-0293","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,7]]}}}