BACKGROUND COVID-19, a disease caused by SARS-CoV-2, has posed a threat to global public health. This retrospective study of 5127 patients with COVID-19 admitted to an Emergency Department in Poland between March 2020 and April 2021 aimed to identify risk factors for severe disease and mortality using the modified early warning score (MEWS). MATERIAL AND METHODS The study was based on a retrospective analysis of patients with SARS-CoV-2 infection admitted to the Emergency Department between March 2020 and April 2021. A total of 5127 cases were included in the final analysis. Identifying the group of high-risk patients with COVID-19 was determined based on the MEWS score. RESULTS Most of the patients studied were male (53.38%). The in-hospital mortality rate among the patients was 21.53%. The factors associated with the risk of in-hospital mortality from COVID-19 were age (>60 years, hazard ratio [HR]=2.27, P<0.001), comorbidities (cancer, HR=1.39, P=0.005; heart failure, HR=1.31, P=0.009; renal failure, HR=1.37, P=0.004), higher MEWS score (MEWS ≥5, HR=1.43, P<0.001), higher percentage of lung parenchyma affected (>50%, HR=2.10, P=0.001), and higher respiratory rate (>24 breaths per min, HR=2.10, P<0.001). CONCLUSIONS This study produced real-world data of risk factors for mortality from COVID-19 and the use of the MEWS for a faster identification of patients with COVID-19 requiring more intensive medical care.