Effect of COVID-19 Vaccination on Survival of Iranian Patients: comparison of Cox Regression, Survival Tree and Forests

The effectiveness of COVID-19 vaccination determines the resource allocation for saving lives in this pandemic. Certainly, the efficacy of all vaccines has been studied in laboratory situations. However, the present study aims to estimate the effectiveness of vaccination in real conditions of Iranian populations by controlling the effect of demographic factors and the history of chronic diseases. This historical cohort study used information on 1988 hospitalized COVID-19 patients with less than 93% blood oxygen levels. Cox regression, Survival Tree, and Forests were applied to estimate the effect of immunity from vaccination on survival, while the effect of demographic characteristics and history of chronic diseases was controlled. The analysis showed that 10% of the patients were immunized, while the Sinopharm vaccine and the rest by Sputnik induced 86% of the immunity. Although there was no difference in the effectiveness of the vaccines, it was found that the immunity from each vaccine increased survival. Patient age was identified as the most influential factor in survival. Other contributing factors include the history of opium/smoking, cancer, the history of chronic lung disease, kidney disease, high blood pressure, and cardiovascular problems. Although age is the most influential factor in patient survival, immunity can control the risk of COVID-19. Therefore, it is recommended to prioritize the old and patients with any of the above underlying problems for vaccination and timely treatment.