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

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