Abstract
Background
Although the SARS-CoV-2 Omicron variant is considered to induce less severe disease, there have been no consistent results on the extent of the decrease in severity.
Objectives
To compare the clinical outcomes of COVID-19–positive patients with Omicron and Delta variant infection.
Data sources
Searches were implemented up to 8 November 2022 in PubMed, Web of Science, BioRvix, and MedRvix.
Study eligibility criteria
Eligible studies were cohort studies reporting the clinical outcomes of COVID-19–positive patients with Omicron and Delta variant infection, including hospitalization, intensive care unit (ICU) admission, receiving invasive mechanical ventilation (IMV), and death.
Participants
COVID-19–positive patients with Omicron and Delta variant infection.
Assessment of risk of bias
Risk of bias was assessed employing the Newcastle-Ottawa Scale.
Methods of data synthesis
Random-effect models were employed to pool the ORs and 95% CIs to compare the risk of clinical outcome. I2 was employed to evaluate the heterogeneity between studies.
Results
A total of 33 studies with 6 037 144 COVID-19–positive patients were included in this meta-analysis. In the general population of COVID-19–positive patients, compared with Delta, Omicron variant infection resulted in a decreased risk of hospitalization (10.24% vs. 4.14%, OR = 2.91, 95% CI = 2.35–3.60), ICU admission (3.67% vs. 0.48%, OR = 3.64, 95% CI = 2.63–5.04), receiving IMV (3.93% vs. 0.34%, OR = 3.11, 95% CI = 1.76–5.50), and death (2.40% vs. 0.46%, OR = 2.97, 95% CI = 2.17–4.08). In the hospitalized patients with COVID-19, compared with Delta, Omicron variant infection resulted in a decreased risk of ICU admission (20.70% vs. 12.90%, OR = 1.63, 95% CI = 1.32–2.02), receiving IMV (10.90% vs. 5.80%, OR = 1.65, 95% CI = 1.28–2.14), and death (10.72% vs. 7.10%, OR = 1.44, 95% CI = 1.22–1.71).
Conclusions
Compared with Delta, the severity of Omicron variant infection decreased.