The Change in Demographic and Clinical Features of Hospitalized Omicron Patients After the Pandemic: A Territory-wide Retrospective Cohort Study (Preprint)

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.