Systematic review
Clinical outcomes of the severe acute respiratory syndrome coronavirus 2 Omicron and Delta variant: systematic review and meta-analysis of 33 studies covering 6 037 144 coronavirus disease 2019–positive patients

https://doi.org/10.1016/j.cmi.2023.03.017Get rights and content

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.

Keywords

Delta
Hospitalization
Meta-analysis
Omicron
SARS-CoV-2

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