Severity of COVID-19 among Hospitalized Patients: Omicron Remains a Severe Threat for Immunocompromised Hosts

Louis Nevejan, Sien Ombelet, Lies Laenen, Els Keyaerts, Thomas Demuyser, Lucie Seyler, Oriane Soetens, Els Van Nedervelde, Reinout Naesens, Dieter Geysels, Walter Verstrepen, Lien Cattoir, Steven Martens, Charlotte Michel, Elise Mathieu, Marijke Reynders, Anton Evenepoel, Jorn Hellemans, Merijn Vanhee, Koen MagermanJustine Maes, Veerle Matheeussen, Hélène Boogaerts, Katrien Lagrou, Lize Cuypers, Emmanuel André

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The Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in the general population in the context of a relatively high immunity gained through the early waves of coronavirus disease 19 (COVID-19), and vaccination campaigns. Despite this context, a significant number of patients were hospitalized, and identifying the risk factors associated with severe disease in the Omicron era is critical for targeting further preventive, and curative interventions. We retrospectively analyzed the individual medical records of 1501 SARS-CoV-2 positive hospitalized patients between 13 December 2021, and 13 February 2022, in Belgium, of which 187 (12.5%) were infected with Delta, and 1036 (69.0%) with Omicron. Unvaccinated adults showed an increased risk of moderate/severe/critical/fatal COVID-19 (crude OR 1.54; 95% CI 1.09–2.16) compared to vaccinated patients, whether infected with Omicron or Delta. In adults infected with Omicron and moderate/severe/critical/fatal COVID-19 (n = 323), immunocompromised patients showed an increased risk of in-hospital mortality related to COVID-19 (adjusted OR 2.42; 95% CI 1.39–4.22), compared to non-immunocompromised patients. The upcoming impact of the pandemic will be defined by evolving viral variants, and the immune system status of the population. The observations support that, in the context of an intrinsically less virulent variant, vaccination and underlying patient immunity remain the main drivers of severe disease.
Original languageEnglish
Article number2736
Issue number12
Publication statusPublished - 8 Dec 2022

Bibliographical note

Funding Information:
UZ Leuven, as national reference center for respiratory pathogens, is supported by Sciensano, the Belgian national institute of health, which is gratefully acknowledged. All members of the Belgian SARS-CoV-2 genomic consortium are gratefully acknowledged.

Publisher Copyright:
© 2022 by the authors.

Copyright 2023 Elsevier B.V., All rights reserved.


  • Covid-19
  • Omicron
  • Delta
  • Immunocompromised host
  • hospitalisation


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