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. 2024 Jul;12(7):e1269.
doi: 10.1002/iid3.1269.

Risk of intensive care unit admission and mortality in patients hospitalized due to influenza A or B and SARS‑CoV‑2 variants Omicron or Delta

Omid Rezahosseini  1 , Casper Roed  1   2   3 , Adin Sejdic  1   2 , Mads Frederik Eiberg  1 , Lene Nielsen  4 , Jonas Boel  4 , Caroline Klint Johannesen  5 , Maarten van Wijhe  3 , Kristina Træholt Franck  6 , Sisse Rye Ostrowski  2   7 , Birgitte Lindegaard  1   2 , Thea K Fischer  3   5   6   8 , Troels Bygum Knudsen  1 , Jon Gitz Holler  1 , Zitta Barrella Harboe  1   2   6 ; COVID‐19 Omicron Delta study group collaborators
Collaborators, Affiliations

Risk of intensive care unit admission and mortality in patients hospitalized due to influenza A or B and SARS‑CoV‑2 variants Omicron or Delta

Omid Rezahosseini et al. Immun Inflamm Dis. 2024 Jul.

Abstract

Background: Respiratory viral infections have significant global health impacts. We compared 30-day intensive care unit (ICU) admission and all-cause mortality risks in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta and Omicron variants versus influenza A and B (A/B).

Methods: Data from two retrospective inpatient cohorts in Capital Region of Denmark were analyzed. Cohorts included hospitalized influenza A/B patients (2017-2018) and SARS-CoV-2 Delta/Omicron patients (2021-2022), aged ≥18 years, admitted within 14 days of a positive real-time polymerase chain reaction test result. Cumulative ICU admission and mortality rates were estimated using the Aalen-Johansen estimator. Cox regression models calculated hazard ratios (HRs) for ICU admission and mortality.

Results: The study encompassed 1459 inpatients (Delta: 49%; Omicron: 26%; influenza A: 6.4%; and influenza B: 18%). Cumulative incidence of ICU admission was 11%, 4.0%, 7.5%, and 4.1%, for Delta, Omicron, influenza A, and B, respectively. For ICU admission, adjusted HRs (aHRs) were 3.1 (p < .001) and 1.5 (p = .34) for Delta and Omicron versus influenza B, and 1.5 (p = .36) and 0.71 (p = .48) versus influenza A. For mortality, aHRs were 3.8 (p < .001) and 3.4 (p < .001) for Delta and Omicron versus influenza B, and 2.1 (p = .04) and 1.9 (p = .11) versus influenza A.

Conclusion: Delta but not Omicron inpatients had an increased risk for ICU admission compared to influenza B; however, both variants were associated with higher risks of mortality than influenza B. Only Delta inpatients had a higher risk of mortality than influenza A inpatients.

Keywords: SARS‐CoV‐2 Delta variants; SARS‐CoV‐2 Omicron variant; influenza A; influenza B; intensive care units; mortality.

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Conflict of interest statement

O. R. received a grant from Rigshospitalet and a grant from A. P. Møller Fonden not related to this work. Mads Ejberg has received research funding from the Danish Cancer Society (grant number KBVU‐M. S. R320‐A18526). K. T. F. has received grants from the Lundbeck Foundation (grant number R349‐2020‐835). Z. B. H. received grants from the Independent Research Fund (grant number 0134‐00257B), the Lundbeck Foundation (grant number R349‐2020‐835), the Helen Rudes Foundation, and the Danish Cancer Society (grant number KBVU‐MS R327‐A19137).

Figures

Figure 1
Figure 1
Cumulative incidence of ICU admission within 30 days after hospitalization. The cumulative incidence of ICU admission at day 30 after hospitalization was 11% (95% confidence interval [CI], 8.2–13%), 4.0% (95% CI, 2.0–5.9%), 7.5% (95% CI, 2.1–13%), and 4.1% (95% CI, 1.7–6.5%) for patients with SARS‐CoV‐2 Delta, SARS‐CoV‐2 Omicron, influenza A, and influenza B infections, respectively (p < .001).
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