The Effect of COVID-19 Vaccination on Reducing the Risk of Infection, Hospitalization, and Death in Isfahan Province, Iran

Abstract

Background: We aimed to evaluate the effect of COVID-19 vaccines in preventing infection, hospitalization, and mortality due to COVID-19 in Isfahan Province, Iran. Methods: Following a retrospective cohort design, data of all vaccinated individuals since the rollout of vaccination of the general population are analyzed, Mar 2020 to Aug 13, 2021. Moreover, the data of all non-vaccinated people were collected by the census method for this period. The two groups were compared concerning hospitalization and mortality using the Chi-square test. Kaplan-Meyer was also used to calculate the median interval between receiving a vaccine and outcome (hospitalization and death). Results: Overall, 583434 people have received a second dose of a vaccine from Mar 2020 to Aug 2021, which 74 (n=433403) was Sinopharm, 18.2 (n=106027) AstraZeneca, 3.6 (n=21216) Sputnik, and 3.9 (n=22,788) Barekat. In contrast, 2,551,140 people living in the Isfahan Province did not receive a vaccine. The median interval between injection of the first dose and the hospitalization for those who received Sinopharm, AstraZeneca, Sputnik, and Barekat was 22, 61, 19, and 19 days, respectively. For unvaccinated cases, the rates of infection, hospitalization, and mortality (per 1000 population) were 69.7, 12.1, and 1.04, respectively. In contrast, for vaccinated individuals, these rates were 3.9, 1.08, and 0.09, two weeks after the second dose, respectively. Conclusion: The highest and lowest reduction in relative risk was for those who received AstraZeneca and Sputnik, respectively.