Relationship between primary vaccination coverage and booster coverage against COVID-19, socio-economic indicators, and healthcare structure in Brazil

OBJECTIVE: To investigate the relationship between vaccination coverage and booster coverage against COVID-19, socio-economic indicators, and healthcare structure in Brazil. STUDY DESIGN: This is a nationwide population-based ecological study. METHODS: We have obtained data on COVID-19 vaccination for each Brazilian state until December 22, 2022. Our outcomes of interest were primary and booster vaccination coverage. The independent variables included: human development index (HDI); Gini index; population density; unemployment rate; percentage of the population covered by primary health care (PHC); percentage of the population covered by community health workers; number of family health teams; and number of public health establishments. Statistics were performed by using a multivariable linear regression model. RESULTS: Lower rates of primary vaccination coverage were found in states with lower HDI (P = 0.048), population covered by PHC (P = 0.006), and number of public health establishments (P = 0.004). Lower rates of booster coverage were also found in states with lower population density (first booster: P = 0.004; second booster: P = 0.022), PHC (first booster: P = 0.033; second booster: P = 0.042), and public health establishments (first booster: P < 0.001; second booster: P = 0.027). CONCLUSION: Our findings showed heterogeneity in access to vaccination against COVID-19 in Brazil, with lower vaccination coverage in localities with the worst socio-economic indicators and limited healthcare resources.