Retrospective analysis of epidemiologic features and clinical course of COVID-19 patients and comparison between vaccinated and unvaccinated patients.

At our Pneumology Department, we dealt with three waves of COVID-19 pandemics. The purpose of this study is to compare patients' epidemiological and clinical characteristics across waves and to assess the effect of vaccination on clinical presentation, course, and prognosis. From March 2020 to March 2022, a retrospective cohort study was conducted to compare patient characteristics. Based on the time of hospital admission, data from 456 patients were collected and divided into three groups [first wave (IW), second wave (IIW), and third wave (IIIW)]. In addition, we looked at the link between vaccination, clinical presentation and hospitalization outcome. The average age and comorbidities of patients increased, as did the worsening of respiratory conditions at admission (partial pressure of oxygen/fraction of inspired oxygen ratio median 207 in IW, 95.5 in IIW, and 99 in IIIW). Continuous positive airway pressure was the primary respiratory support during the first wave, but an increase in the use of high-flow nasal cannula and non-invasive ventilation was later observed, resulting in a higher hospital discharge rate and a lower intubation rate. Vaccinated patients had less severe COVID-19-related respiratory failure, a better clinical course, and a higher hospital discharge rate (71.4% in the vaccinated group vs. 44.7% in the non-vaccinated group, p<0.001). Patients' characteristics changed over the three waves, possibly due to virus mutations. The advancement of clinical and therapeutic management knowledge has contributed to a reduction in the severity of respiratory failure. The vaccination campaign improved the clinical course and reduced mortality.