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Meta-Analysis
. 2023 Jul;29(7):835-844.
doi: 10.1016/j.cmi.2023.03.017. Epub 2023 Mar 18.

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

Fei-Hong Hu  1 , Yi-Jie Jia  1 , Dan-Yan Zhao  1 , Xue-Lei Fu  1 , Wan-Qing Zhang  1 , Wen Tang  1 , Shi-Qi Hu  1 , Hua Wu  1 , Meng-Wei Ge  1 , Wei Du  1 , Wang-Qin Shen  1 , Bin Zhu  2 , Hong-Lin Chen  3
Affiliations
Meta-Analysis

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

Fei-Hong Hu et al. Clin Microbiol Infect. 2023 Jul.

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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Figures

Fig. 1
Fig. 1
Flowchart of the study selection process. ICU, intensive care unit; IMV, invasive mechanical ventilation.
Fig. 2
Fig. 2
Meta-analysis of the association of Delta or Omicron SASR-CoV-2 with hospitalization in the general population of COVID-19 positive.
Fig. 3
Fig. 3
Meta-analysis of the association of Delta or Omicron SASR-CoV-2 with ICU admission in the general population of COVID-19 positive. ICU, intensive care unit.
Fig. 4
Fig. 4
Meta-analysis of the association of Delta or Omicron SASR-CoV-2 with receiving IMV in the general population of COVID-19 positive. IMV, invasive mechanical ventilation.
Fig. 5
Fig. 5
Meta-analysis of the association of Delta or Omicron SASR-CoV-2 with mortality risk in the general population of COVID-19 positive.
Fig. 6
Fig. 6
Meta-analysis of the association of Delta or Omicron SASR-CoV-2 with ICU admission in the hospitalized patients with COVID-19 positive. ICU, intensive care unit.
Fig. 7
Fig. 7
Meta-analysis of the association of Delta or Omicron SARS-CoV-2 with receiving IMV in the hospitalized patients with COVID-19 positive. IMV, invasive mechanical ventilation.
Fig. 8
Fig. 8
Meta-analysis of the association of Delta or Omicron SASR-CoV-2 with mortality risk in the hospitalized patients with COVID-19 positive.
See this image and copyright information in PMC

References

    1. Graham M.S., Sudre C.H., May A., Antonelli M., Murray B., Varsavsky T., et al. Changes in symptomatology, reinfection, and transmissibility associated with the SARS-CoV-2 variant B.1.1.7: an ecological study. Lancet Public Health. 2021;6:e335–e345. doi: 10.1016/s2468-2667(21)00055-4. - DOI - PMC - PubMed
    1. Del Rio C., Malani P.N., Omer S.B. Confronting the Delta variant of SARS-CoV-2, summer 2021. JAMA. 2021;326:1001–1002. doi: 10.1001/jama.2021.14811. - DOI - PubMed
    1. Kupferschmidt K., Wadman M. Delta variant triggers new phase in the pandemic. Science. 2021;372:1375–1376. doi: 10.1126/science.372.6549.1375. - DOI
    1. Wang Y., Chen R., Hu F., Lan Y., Yang Z., Zhan C., et al. Transmission, viral kinetics and clinical characteristics of the emergent SARS-CoV-2 Delta VOC in Guangzhou, China. EClinicalMedicine. 2021;40 doi: 10.1016/j.eclinm.2021.101129. - DOI - PMC - PubMed
    1. Liu C., Ginn H.M., Dejnirattisai W., Supasa P., Wang B., Tuekprakhon A., et al. Reduced neutralization of SARS-CoV-2 B.1.617 by vaccine and convalescent serum. Cell. 2021;184:4220–4236.e13. doi: 10.1016/j.cell.2021.06.020. - DOI - PMC - PubMed

Supplementary concepts