Severity of the New UK SARS-Cov2 Variant in COVID-19 Infection

SEVASAR is a paired cohort study with retrospective data collection: * Presentation: patients hospitalized for COVID-19 with SARS-CoV-2 variant 20I / 501Y.V1 * Not exposed: patients hospitalized for COVID-19 with SARS-CoV-2 corresponding to wild variants type 20A. EU1 or 20A. EU2 The severity of illness will be compared between pairs. Disease severity will be assessed according to the following definition: defined by a composite criterion including, at 28 days after hospital admission: WHO scale \>5 /11 levels, (death OR need for invasive ventilation OR need for high flow ventilation (Optiflex or NIV or CPAP) or high concentration mask. This event will be taken into account regardless of its time of occurrence between the first day of the hospitalization studied and D29 after hospital admission.