Abstract
BACKGROUND: With frequent new variants of SARS-CoV-2 and vaccine coverage below 50 % in low-income countries, COVID-19 remains a global health challenge, underscoring the need to update evidence-based health strategies and to understand the pandemic from a historical standpoint. Brazil is an important model for study because of the initial widespread infection and subsequent high population adherence to vaccination. OBJECTIVE: To compare severity outcomes in a setting of initial low vaccination and after mass vaccination (> 95 %) according to COVID-19 test positivity. METHODS: A prospective study with 673 patients tested for COVID-19, followed up until final outcome, in an isolation unit in southern Brazil. We compare the main outcomes and symptoms between the three epidemic waves in Brazil. RESULTS: The vaccination coverage was 0.4 %, 35.0 %, and 97.6 % during the three waves, while severe cases decreased significantly from the first to the third. Black and brown ethnicity were more frequent among cases during the second wave, and lower income was associated with the second and third. In the multivariate analysis, higher heart rate and black and brown ethnicity were new factors associated with positive diagnosis and severity independently of period. CONCLUSIONS: As vaccination progressed, ethnicity and lower income emerged as increasingly important risk factors, uncovering complex relationships between vaccine coverage and access to information in Brazil. The present results offer a broad view of the clinical features of COVID-19 over almost the entire pandemic period and can help evaluate public policies for subsequent management decisions and strategies to reduce health inequities.