Clinical characteristics and outcome of patients with SARS-CoV-2 Omicron variant in Shanghai: A single center, retrospective, observational study

Background: In March 2022, a severe outbreak of the SARS-CoV-2 Omicron variant occurred in Shanghai. This study aimed to determine disease severity, clinical features, clinical outcome in hospitalized patients with the Omicron variant and evaluate the effectiveness of one-dose, two-dose, and three-dose inactivated vaccines in reducing viral loads, disease course, ICU admissions and severe diseases. Methods: Retrospective cohort analysis was performed on 5,170 adult patients (≥18 years) identified as severe acute respiratory syndrome coronavirus 2 positive with Reverse Transcription Polymerase Chain Reaction admitted at Shanghai Medical Center for Gerontology between March 2022 and June 2022. Demographic information, laboratory data, immunization status, clinical characteristics and outcomes were extracted from electronic medical records. Results: Among 5,170 enrolled patients, the median age was 53 years, and 2,861 (55.3 %) were male. 71.0 % were mild COVID-19 cases, and cough (1,137 [22.0 %]), fever (592 [11.5 %]), sore throat (510 [9.9 %]), and fatigue (334 [6.5 %]) were the most common symptoms on the patient’s first admission. The median length of hospital stay was 8.7 ± 4.5 days. In multivariate logistic analysis, booster vaccination can significantly reduce ICU admissions and decrease the severity of COVID-19 outcome when compared with less doses of vaccine (OR = 0.75, 95 %CI, 0.62–0.91, P ≤ 0.005; OR = 0.99, 95 %CI, 0.99–1.00, p