The primary outcome was in-hospital mortality.<h4>Results</h4>In comparison with vaccinated patients from the fourth wave, unvaccinated patients from the first wave had reduced prevalence of heart disease (35% vs. 56%), renal failure (9% vs. 15%), but higher prevalence of fever at time of diagnosis (84% vs. 59%), malignancy (16% vs. 6%), higher computed tomography (CT) severity visual score, higher CRP (C-reactive protein) serum levels (median value 105 mg/L vs. 75 mg/L), but lower burden of frailty. Here, CRP is linked to kidney failure.