Hospital readmission rates and factors due to COVID-19 reinfections: a registry-based cohort study in Brazil...

COVID-19 vaccination emerged as a key strategy to reduce disease severity and curb the pandemic's spread, proving crucial in preventing complications and hospitalizations. Despite its positive impact, hospital readmissions due to COVID-19 reinfections have been observed, influenced by emerging variants and individual clinical and demographic characteristics. Given the limited evidence on such readmissions, studies based on representative samples are essential to better understand the associated factors. This study aims to analyze the role of vaccination, identify clinical and demographic characteristics associated with readmissions due to COVID-19 reinfections, and estimate the annual readmission rate in Brazil from 2020 to 2022.

This nationwide cohort study included hospitalized individuals reported in the National Influenza Surveillance System with confirmed COVID-19 or unspecified Severe Acute Respiratory Infection (SARI) diagnoses, encompassing approximately 1.9 million Brazilians from 2020 to 2022. Demographic and clinical variables from the first hospitalization and readmission were included, alongside a time-varying ecological vaccination variable. Fine and Gray's proportional subdistribution hazards model, accounting for death as a competing event, was used to assess predictors of hospital readmission. Results were expressed as hazard ratios (HR) with 95% confidence intervals.

The analysis indicated that the vaccination period following 80% first-dose coverage (from December 19, 2021, onward) showed a protective effect against readmission. After adjusting for multiple variables, this protective effect became evident, with a 13% reduction in the risk of readmission in the post-vaccination period compared to the pre-vaccination period (HR: 0.87; 95% CI: 0.85-0.89). In contrast, factors such as female sex, age 60 years or older, and the presence of comorbidities were associated with an increased risk of readmission.

The findings reinforce the critical role of COVID-19 vaccination as a fundamental strategy for reducing reinfections and readmissions. Despite viral mutations, immunization stands out as a significant contributor to population protection.