Patients With Delta vs. Omicron Variants in the Emergency Department

Quick Takes

  • This is a retrospective, observational, multicenter study examining differences in clinical characteristics and outcomes between patients infected with the Omicron and Delta variants of SARS-CoV-2.
  • The study corroborates earlier reports suggesting Omicron infection is associated with less severe disease compared to the Delta variant, independently of differences in clinical characteristics.

Study Questions:

How do clinical characteristics and in-hospital outcomes compare between patients presenting to the emergency department (ED) with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection with the Delta variant versus the Omicron variant?


This retrospective, observational, multicenter study included 3,728 patients ≥16 years old with a positive SARS-CoV-2 test who presented to 13 EDs in the Paris metropolitan area in France from November 29, 2021–January 10, 2022. The authors compared characteristics between those infected with the Delta and Omicron variants, including demographics, medical history, vaccination status, inflammatory markers, vital signs, imaging findings, in addition to outcomes such as intensive care unit (ICU) admission, mechanical ventilation, and in-hospital mortality.


Of 3,728 patients who had a positive SARS-CoV-2 test, 1,716 patients who had a variant determination (818 Delta and 898 Omicron) were included. The median age was 58 years, and 49% were women. Incidental SARS-CoV-2 infection was diagnosed in 23% of patients with Omicron versus 13% of patients with Delta. Patients infected with the Omicron variant were younger (54 vs. 62 years), had a lower rate of obesity (8.0% vs. 12.5%), were more likely to be vaccinated (65% vs. 39% for one dose), had a lower rate of shortness of breath (26% vs. 50%), and were more likely to be discharged home from the ED (59% vs. 37%). C-reactive protein levels were lower in patients with Omicron compared to those with a Delta variant infection. Compared with Delta, the Omicron variant was associated with lower risk for ICU admission (-11.4% difference), mechanical ventilation (-3.6% difference), and in-hospital mortality (-4.2% difference) after adjusting for age, sex, hypertension, obesity, diabetes, chronic respiratory disease, chronic kidney disease, immunosuppression, number of vaccine doses, and center.


Compared with the Delta variant, infection with the Omicron variant in patients in the ED was associated with better in-hospital outcomes, including higher survival.


This study corroborates reports that infection with the Omicron variant of SARS-CoV-2 is associated with less severe clinical features and outcomes compared to infection with the Delta variant. Patients presenting to the ED with Omicron were also younger and more likely to be previously vaccinated. Adjusting for clinical characteristics only minimally attenuated the differences in outcomes between Delta and Omicron infections, suggesting that these differences are likely driven by a relatively lower tendency for Omicron to induce a hyperinflammatory response. Strengths of the study include its multicenter nature, the comprehensive characterization of patients, and the author account for patients incidentally diagnosed with SARS-CoV-2. The study population was, however, limited to those with a variant identified (<50% of the entire cohort), lending a risk of selection bias.

Clinical Topics: Heart Failure and Cardiomyopathies, Noninvasive Imaging, Prevention, Acute Heart Failure, Heart Failure and Cardiac Biomarkers

Keywords: COVID-19, COVID-19 Testing, COVID-19 Vaccines, C-Reactive Protein, Diagnostic Imaging, Dyspnea, Emergency Service, Hospital, Heart Failure, Hospital Mortality, Inflammation, Intensive Care Units, Obesity, Patient Discharge, Primary Prevention, Respiration, Artificial, SARS-CoV-2, Vaccination, Vital Signs

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