Survival of COVID-19 among the Iranian population before and after the Delta variant spread

COVID-19 has been considered the most important issue in the last two years. Some characteristics and factors can play a pivotal role in the survival time and mortality of COVID-19 patients. The Delta variant was one of the most important variants of COVID-19. This study aimed to investigate the risk factors of COVID-19 survival before and after the spread of the Delta variant. In this historical cohort study, 6,117 hospitalized patients with positive COVID-19 PCR tests between January and September 2021 participated. Some characteristics such as age, sex, death by COVID-19, and presence/absence of some comorbidities were registered for the patients. Log-rank test and Cox proportional hazards model were done to check the effect of the potential risk factors on the survival of COVID-19 patients by considering the onset of symptoms to death as the time variable. The mean age of patients was 47.29 (SD=18.70). 53% of patients were female, 4.6% were admitted to the ICU, and 3.6% died from COVID-19. Age (HR=9.81, p<.001), cardiovascular disease (HR=2.86, p<.001), chronic kidney disease (HR=6.21, p<.001), diabetes (HR=2.16, p=0.002), hypertension (HR=2.67, p<.001), ICU admission (HR=12.92, p<.001), pO2<93% (HR=6.75, p<.001), and intubation (HR=21.54, P<.001) were risk factors that were influential on the survival of COVD-19 patients before the spread of the Delta variant. Although the effect of some variables changed after the spread of the Delta variant, some of them, like chronic kidney disease and hypertension were no longer significant. Although the effect of some comorbidities was significant only in the crude models, they were not influential in the adjusted model. Conversely, in the presence of other risk factors, especially age, most of the comorbidities were not significant in the adjusted model. Older age, ICU admission, intubation, and pO2<93% are the most important variables which played a pivotal role in the survival of individuals infected by COVID-19.