Abstract
Introduction: COVID-19 vaccination and its associated complications have been a controversial issue worldwide. This study aimed to identify the determinants of infection leading to hospitalization following COVID-19 vaccination in Chaharmahal and Bakhtiari Province.
Methods: In this case-control study, after screening records from 47,001 individuals, 260 hospitalized vaccinated individuals were selected as cases, while 130 vaccinated outpatients and 130 healthy individuals were included as controls (n = 520). Data were analyzed by Stata 17 using descriptive and inferential statistics, including univariate and multivariable analyses and ordinal logistic regression models.
Results: Multivariable analyses revealed older age (> 55 years, OR = 11.08, P < 0.001), female gender (OR = 0.45, P = 0.002), prior infection (OR = 292.7, P = 0.001), and non-healthcare occupations (OR = 2.07, P = 0.036) as significant risk factors for hospitalization, while being male (OR = 0.45, P = 0.002) and a healthcare worker (OR = 0.22, P = 0.006) were protective. Moreover, the Sinopharm (OR = 2.40, P = 0.012) and other vaccines (OR = 2.54, P = 0.036) were associated with higher hospitalization risk compared to AstraZeneca. Additionally, the protective effect of vaccination and underlying disease decreased over time (underlying disease HR = 0.99, P = 0.014; homologous booster HR = 0.99, P < 0.001; heterologous booster HR = 0.99, P = 0.025).
Conclusion: Age, gender, comorbidities, recent hospitalization, and high-risk occupation influenced COVID-19 hospitalization, while prior infection and vaccination provided temporary protection, underscoring the need for targeted, time-sensitive interventions.