Understanding the Change of In-hospital Mortality and Respiratory Failure Between Delta and Omicron Waves from a Tertiary Hospital in Southern Thailand: A Retrospective Cohort Study

Objectives: This retrospective cohort study aims to assess the incidence and associated factors of in-hospital mortality and respiratory failure among patients with COVID-19 during the Omicron and Delta epidemics.

Methods: We reviewed medical records from a regional hospital in Southern Thailand of patients with COVID-19 during the Delta wave (August 2021 to December 2021) and the Omicron wave (February 2022 to June 2022). A computer-generated random sampling approach was used to select patients for analysis. Logistic regression identified factors associated with respiratory failure, while Cox proportional hazard models were used for in-hospital mortality associations.

Results: Among 5729 hospitalized patients with COVID-19 (Delta: 1229; Omicron: 4500), 1164 were randomly sampled (Delta: 295; Omicron: 869). Patients during the Delta wave were older (median: 52.0; interquartile range: 31.5-70.0) compared with those during the Omicron wave (median: 37.0; interquartile range: 8.0-65.0), with lower rates of completed two doses of vaccination (Delta: 18.3%; Omicron: 51.8%). The Delta variant exhibited higher rates of respiratory failure (46.8% vs Omicron: 22.3%) and in-hospital mortality (12.5% vs Omicron: 6.9%). Increased age (adjusted odds ratio [aOR] 1.04, 95% confidence interval [CI] 1.03-1.04), severity at admission (aOR 12.48, 95% CI 7.21-22.22), and delayed time to admission (aOR 1.07, 95% CI 1.02-1.12) increased the risk of respiratory failure, while receiving two-dose vaccination reduced this risk (aOR 0.36, 95% CI 0.24-0.53). Similarly, increased age (adjusted hazard ratio [aHR] 1.05, 95% CI 1.03-1.06), severity at admission (aHR 7.20, 95% CI 4.09-12.60), and delayed time to admission (aHR 1.05, 95% CI 1.00-1.11) were associated with higher in-hospital mortality, with two-dose vaccination decreasing this risk (aHR 0.45, 95% CI 0.27-0.75).

Conclusions: The Delta variant exhibited higher in-hospital mortality and respiratory failure rates compared with Omicron. The identification of high-risk groups emphasizes the critical need for timely care for vulnerable patients. Timely access to care and vaccination coverage are crucial in reducing respiratory failure and mortality due to COVID-19, highlighting the necessity for tailored interventions to mitigate the impact of emerging variants.