Comparative Analysis of COVID-19 Severity and Mortality Among Vaccinated and Unvaccinated Individuals During the Delta Variant Surge in a Tertiary Care Center

Introduction: On March 11, 2020, the World Health Organization (WHO) declared Coronavirus disease 2019 (COVID-19) as a pandemic. The spread of the Delta variant of coronavirus started in June 2021 and accounted for the fifth peak of COVID-19 in Iran in July 2021. According to reports from other countries, vaccination protects against severe diseases caused by COVID-19, including the Delta variant. Studies have also shown that vaccination provides strong protection against SARS-CoV-2 infection, COVID-19-related hospitalization, and mortality. This retrospective cohort study was designed based on the medical care monitoring center (MCMC) database of Sayyad Shirazi Hospital. Methods: The following patient data were extracted for this study: demographic characteristics, signs and symptoms, ICU admission, need for aggressive oxygen therapy, including intubation, mortality, and vaccination status. Results: Being vaccinated was associated with a 4.14-fold increase in survival (adjusted OR=4.14; 95% CI: 2.22 to 7.69; P<0.01), and individuals in a younger age group demonstrated a 5.58-fold higher likelihood of surviving (adjusted OR=5.58; 95% CI: 4.25 to 8.14; P<0.01). The risk of severe COVID-19 was significantly lower in vaccinated individuals, showing a 3.12-fold decrease in risk (adjusted OR=3.12; 95% CI: 2.06 to 4.72; P<0.01), and in younger age groups, the risk exhibited a 3.28-fold decrease (adjusted OR=3.28; 95% CI: 2.66 to 4.04; P<0.01). Conclusion: The present results suggest that receiving at least one dose of COVID-19 vaccine had a significant relationship with decreased COVID-19 severity and mortality in vaccinated patients compared to unvaccinated patients.