Increasing Prevalence of Occult HBV Infection in Adults Vaccinated Against Hepatitis B at Birth

Background/Objectives: Immunization with the hepatitis B vaccine is the most effective means of preventing acute HBV infection. However, whether the primary vaccination of infants confers lifelong immunity remains controversial. Therefore, the ongoing surveillance of vaccine recipients is required. Methods: A longitudinal study was carried out based on LongAn county, one of the five clinical trial centers for hepatitis B immunization in China in the 1980s. Serum samples were collected and tested for HBV serological markers and DNA. Results: A total of 637 subjects born in 1987–1993 were recruited, including 503 males and 134 females. The total prevalence of HBsAg was 3.9%. The prevalence in females (8.2%) was significantly higher than that in males (2.8%) (p = 0.004). The prevalence of anti-HBc in females (52.2%) was also significantly higher than that in males (41.2%) (p = 0.021). The prevalence of anti-HBs was 42.7% and did not differ significantly between males (41.7%) and females (46.3%) (p = 0.347). Compared to data from surveillance over the last ten years, the positivity rate of HBsAg did not increase. The positivity rate of anti-HBs decreased significantly (p = 0.049) while that of anti-HBc increased significantly (p = 0.001). The prevalence of occult HBV infection (OBI) in 2024 (6.0%) was significantly higher than that in 2017 (1.6%) (p = 0.045). Subjects diagnosed with OBI in 2017 maintained occult infection in 2024. Conclusions: Neonatal HBV vaccination maintained effective protection for at least 37 years. However, the prevalence of OBI increases with age in those vaccinated at birth, raising a new issue of how to prevent and control OBI in the post-universal infant vaccination era.