The Impact of Early Phase COVID-19 Vaccination on Hospitalized COVID-19 Patients

The number of cases of coronavirus disease-2019 (COVID-19) globally is over 225 million, and diseaserelated deaths are over 4 million. The type, prevalence, and antibody susceptibility of the virus variants of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) and the vaccination rate and coverage are considered critical factors in the progress of COVID-19. We aimed to compare the clinical and laboratory parameters of the patients hospitalized due to COVID-19 in pre-vaccination and post-vaccination periods. We conducted this retrospective cross-sectional study in a tertiary clinic in Turkey. The files of the patients over the age of 18, whose real-time polymerase chain reaction (RT-PCR) tests were positive and who were hospitalized before (November-December 2020, Group 1) and after (March-April 2021, Group 2) COVID- 19 vaccination were scanned. Patients' demographical data, clinical severity, laboratory parameters, thorax computed tomography involvement, and mortalities were recorded. The obtained data were compared among the groups. 601 patients (344 male, 57% and 257 female, 43%) were included in the study. It was observed that the patients in the Group 2 were younger (60.71 +/- 14.06 vs. 66.95 +/- 14.57, p < 0.001), and a significant decrease in mortality [83 (28.6%) vs.139 (44.6%), p = 0.001] were observed in Group 2. The number of patients who needed ventilatory support and the rate of pulmonary involvement was lesser in Group 2, but the difference was non-significant. C-reactive protein, D-dimer, procalcitonin levels were significantly lower in Group 2 patients. Our study shows that the age and mortality of hospitalized COVID-19 patients decreased significantly after vaccination. An increase in the number of booster doses in individuals with advanced age (age > 75) and comorbidity (especially malignancy) may contribute to the control of the disease and immunity in this population.