Accepted for/Published in: JMIR Public Health and Surveillance
Date Submitted: Apr 8, 2025
Date Accepted: Dec 2, 2025
Warning: This is an author submission that is not peer-reviewed or edited. Preprints - unless they show as "accepted" - should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information.
The Change in Demographic and Clinical Features of Hospitalized Omicron Patients After the Pandemic: A Territory-wide Retrospective Cohort Study
ABSTRACT
Background:
The Omicron variant of SARS-CoV-2 underwent several mutations since it was first identified in November 2021, with a large case of outbreak in Hong Kong during early 2022. Yet, local cases of Omicron infections persist, even though COVID-19 ended in May 2023. Therefore, this study aims to compare the changes in clinical and demographic characteristics of hospitalized COVID-19 patients during the Omicron outbreak in Hong Kong.
Objective:
The primary objective compared different strains, while the secondary objective compared during and post-pandemic.
Methods:
This cohort study collected data on COVID-19 infected patients admitted to public hospitals in Hong Kong between the 1st May 2022 and 31st May 2024. Later categorized into 3 periods based on the Omicron strain. Subsequent descriptive analysis was conducted on each characteristic to identify any significant differences between (primary objective) and within (secondary objective) periods.
Results:
136,544 episodes of COVID-19 were identified with 72,471 episodes that occurred during period 1, 41,167 during period 2, and 22,906 during period 3. Notably, the case-fatality ratio increased from 6.3 to 6.4. Demographic characteristics were significantly different between periods for age (0-17 years old, 18-64 years old, ≥85 years old: Adjusted P<.001), sex (Adjusted P<.001), Charlson Comorbidity Index score (0: Adjusted P=.04, 1: Adjusted P=.003), comorbidities (type 2 diabetes mellitus: Adjusted P<.001), race (Pakistani: Adjusted P<.001), length of hospital stay (Adjusted P<.001), social deprivation index (Most disadvantaged: Adjusted P<.001) Clinical characteristics were also significantly different between periods in levels of blood biomarkers (Albumin, Neutrophil, Lymphocyte, Platelet: Adjusted P<.001) and in-patient drug administration (ACE inhibitors, antidiabetics, antiplatelets and anticoagulants, beta blockers, bronchodilators, calcium channel blockers, diuretics, inhaled corticosteroids, rheumatoid drugs, statins, systemic corticosteroids: Adjusted P<.001). Post-hoc results comparing within-groups showed a spill-over into the post-pandemic era in adults (Adjusted P=.91), type 2 diabetes mellitus (Adjusted P=1.00), Pakistani (Adjusted P=.61), and 0 CCI score (Adjusted P=.18).
Conclusions:
Despite the decreasing incidence of Omicron cases admitted to public hospitals in Hong Kong, the increasing case-fatality ratio suggests long-term surveillance of COVID-19 should be maintained to prepare for potential mutations and outbreaks.
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