Rehospitalization due to COVID-19 reinfection in Rio de Janeiro, 2020-2022: Associations with vaccination status, sociodemographic and clinical factors.

The COVID-19 pandemic posed significant challenges, including rehospitalization of patients due to SARS-CoV-2 reinfection, particularly in the context of variants of concern and Brazil's COVID-19 vaccination campaign. This study aimed to estimate the rate of rehospitalizations due to reinfection in the municipality of Rio de Janeiro (2020-2022), assess the impact of individual vaccination status, and identify factors associated with this outcome. Cohort study including individuals aged 18 years or older who were hospitalized with Severe Acute Respiratory Illness (SARI) resulting from SARS-CoV-2 infection in Rio de Janeiro. Data from four administrative databases (SIPNI, e-SUS Notifica, SIVEP-Gripe, and SIM) were integrated through record linkage. Rehospitalizations due to reinfection were defined as those occurring ≥90 days after the initial hospitalization. Annual rehospitalization rates were calculated per 100 person-years. The analysis included demographics, hospital discharge disposition, and vaccination-related variables. Cox proportional hazards models with deaths considered as competing risks were used. Of the 59,001 individuals included, 1,957 (3.3%) experienced rehospitalization. The main finding was that a complete vaccination regimen with a booster (≥3 doses) was associated with a 39% reduction in the risk of rehospitalization (sHR: 0.61; 95% CI: 0.52-0.73), while older age, multimorbidity, and Black race/skin color emerged as significant risk factors. Full vaccination with booster doses offered protection against COVID-19-related rehospitalization; however, racial inequities, advanced age, and comorbidities remain important risk factors. Public health policies that expand periodic booster vaccination, strengthen health education, and address social vulnerabilities are urgently needed as a fundamental strategy for preventing future pandemics.