SARS-CoV-2 Delta and Omicron Variants: Comparative Analysis of Confirmed Cases in Multi-Profile Hospital in Bulgaria

The highly transmissible variants of SARS-CoV-2, Delta (В.1.617.2) and Omicron (В.1.1.529), emerged as "variants of concern" (VOCs) during the COVID-19 pandemic. The aim of this study was to perform a comparative analysis of the confirmed SARS-CoV-2 Delta and Omicron cases among the patients of Uni Hospital (Panagyurishte, Bulgaria). A total of 240 samples out of 2,373 PCR-positive samples collected from COVID-19 patients for the period from 1st July 2021 to 4th February 2022 were analyzed at NCIPD by whole genome sequencing to determine the viral variant. The Delta variant was confirmed for 103 patients, while Omicron for 137 patients. The analysis showed that 6/103 of the Delta variant cases belonged to hospitalized and unvaccinated patients with comorbidities, at a mean age of 68.8 years, two of whom had a lethal outcome. The Omicron cases were mainly in ambulatory patients (136/137), with only one hospitalized. The largest number of Omicron infected patients were in the age group of under 20 years; respectively, this age range had the lowest number of Delta variant cases. The Delta variant was the dominating SARS-CoV-2 variant in the period July 2021 - December 2021; however, it was subsequently displaced by Omicron domination. COVID-19 associated mortality remains one of the most important clinical outcomes.