From Hyperendemic to Low Endemicity: The Effect of Hepatitis B Vaccination on HBV and HDV Prevalence in the Brazilian Amazon

The Amazon Basin was historically hyperendemic for HBV and HDV, associated with severe outcomes like fulminant hepatitis. Brazil initiated its hepatitis B vaccination in 1989. This study assessed the current prevalence in this endemic region to evaluate the impact of vaccination. A cross-sectional population-based survey enrolled 1100 urban and rural residents. HBsAg prevalence was 1.5%, with no cases in individuals under 20 years, demonstrating interrupted vertical and horizontal transmission. Anti-HBc positivity (30.9%) indicated past exposure, predominantly in those over 30 years. Isolated anti-HBc (10.3%) included two occult HBV infections. HDV coinfection occurred in 25% of HBsAg-positive cases, with HDV RNA detected in two. Anti-HDV positivity was exclusive to adults over 30. Vaccination coverage was poorly documented, but 23.7% had protective anti-HBs titers. HBV vaccination has reduced HBsAg prevalence from high to low endemicity in the region, eliminating chronic infections in younger generations. Persistent HDV in older age groups underscores the need for targeted screening. Despite vaccination record gaps, the findings highlight the program's success in interrupting transmission and support continued efforts toward HBV/HDV elimination.