Vaccination inequality and social determinants in Brazil during the COVID-19 pandemic

Brazils vast geographic and socioeconomic diversity has contributed to heterogeneous responses to the COVID-19 pandemic, particularly regarding vaccine distribution. This ecological study examined inequality in COVID-19 vaccine administration across 5,568 Brazilian municipalities from 2021 to 2023. Vaccination coverage was estimated using the vaccination coefficient, and inequality was assessed via the Gini index. We further analyzed associations between vaccine distribution inequality and socioeconomic indicators, including the Social Vulnerability Index (SVI), and the national health infrastructure metric PQAVS-03, using beta regression models. Results indicated that northern states such as Roraima, Para, and Amazonas consistently exhibited the highest Gini coefficients, reflecting marked disparities in vaccine allocation, while southern states like Rio Grande do Sul and Espirito Santo demonstrated more equitable distribution. SVI was significantly associated with vaccine inequality in 2021 and 2022 (p < 0.05), but this association weakened in 2023, suggesting a temporal trend toward greater equity. PQAVS-03 showed no statistically significant association in any year. These findings underscore the persistent impact of structural social determinants on vaccine access during public health emergencies, while also highlighting the potential of Brazils public health system to reduce disparities over time.