Comparative Study of Outcomes of COVID-19 Infection in Vaccinated and Unvaccinated Patients- A Retrospective Analysis

Introduction: Vaccine development was the highest priority during the Coronavirus disease 2019 (COVID-19) pandemic. An ideal vaccine should decrease the risk of infection and reduce the incidence and severity of the disease. Risk of disease or infection following COVID-19 vaccination needs to be evaluated for its efficacy and effectiveness. Aim: To compare the severity of the disease, oxygen requirement, and mortality between vaccinated and unvaccinated COVID-19 patients. Materials and Methods: This retrospective study was done on the data of the patients who were admitted to Nizams Institute of Medical Sciences. All the admitted patients with COVID-19 disease, diagnosed by either Reverse Transcriptase Polymerase Chain Reaction (RTPCR) or rapid antigen detection method from April 2021 to October 2021, were included. Parameters recorded were: age, gender, co-morbidities, clinical staging as per institute protocol, vaccination status, oxygen requirement, the requirement of non invasive or invasive ventilation, inflammatory markers like C-Reactive Protein (CRP), ferritin, D dimer, Computed Tomography (CT) severity index, and outcomes. Results: The mean age of patients was 49.7±14.8 yrs in the unvaccinated group, and 52.75±16.2 yrs in the vaccinated group. Out of 175 patients, 102 (58.28 %) were unvaccinated. There were 25 (14.28%) deaths, of which 20 (80%) were unvaccinated and 5 (20%) were vaccinated. Oxygen requirement was more among the unvaccinated 73/96 (76.04%). High flow oxygen / mechanical ventilation requirement was higher in unvaccinated compared to vaccinated, 38 (76%) vs 12 (24%) respectively (p-value <0.005). The mortality rate was higher in unvaccinated patients with co-morbidity, with an odds ratio of 3.32 (1.2-9.3), p-value=0.02. Serum ferritin levels were significantly higher in the unvaccinated group, 858.15±935.5 vs 473.4±663.2 ng/mL, p-value 0.007. CT severity index in the unvaccinated group was 13.82±5.4, and for the vaccinated group, it was 11.58±5.49. Conclusion: Severe disease, oxygen requirement, and mortality were low in vaccinated patients. Vaccination has also resulted in a statistically significant decrease in mortality in patients with co-morbidities. Serum ferritin levels were also found to be lower in vaccinated patients.