Hospital morbidity and mortality before and after COVID-19 vaccination in Brazil: an interrupted time series analysis

COVID-19, caused by the SARS-CoV-2 virus, presents a wide clinical spectrum, ranging from asymptomatic cases to severe complications such as acute respiratory distress syndrome and thromboembolic events. Mass vaccination has been crucial in reducing morbidity and mortality, but its impact varies across populations due to socioeconomic, demographic, and biological factors. This study analyzed temporal trends in hospital morbidity and mortality due to COVID-19 in Brazil and the impact of mass vaccination. An interrupted time series study was conducted using data from the Influenza Epidemiological Surveillance Information System and the National Immunization Program. Hospitalization and mortality rates due to COVID-19 were analyzed across Brazil’s five major regions from 2020 to 2023. The analysis included corrections for serial autocorrelation and adjustments for SARS-CoV-2 variants of concern (VOCs), such as alpha, gamma, delta, and omicron. Prais-Winsten regression was used to estimate trend changes before and after the start of vaccination. A significant reduction in hospital morbidity and mortality due to COVID-19 was observed after vaccination. Hospitalization rates decreased from 308.7 to 25.1 per 100,000 inhabitants, and mortality rates dropped from 98.7 to 13.6 per 100,000 inhabitants between 2020 and 2023. The North and Northeast regions showed progressive declines, while the Southeast, South, and Central-West regions peaked in 2021. The omicron variant (wave 3) had a significant impact on increasing cases and deaths, even after vaccination. Interrupted time series analysis demonstrated that vaccination positively altered incidence and mortality trends, even in the face of emerging virus variants.