Since the introduction of hepatitis B virus (HBV) vaccines, the numbers of HBV infections and complications have significantly decreased. However, the evidence on whether primary vaccination of infants confers lifelong immunity varies. We aimed to assess long-term immunity among healthcare workers and medical students, and the rate of decline of HBV surface antigen antibodies (anti-HBs). Hepatitis B status among participants born after 1 January 1992 was reviewed at Chulabhorn Royal Academy, Thailand. Participants were stratified by intervals since primary vaccination. HBV immunity was determined and analyzed as anti-HBs decline rate in participants with multiple follow-ups. A total of 464 participants were analyzed, with a median age of 23. Protective immunity against HBV (anti-HBs ≥ 10 mIU/mL) at 16-20, 21-25 and 26-28 years post-primary vaccination was 28%, 51.7% and 60%, respectively. The overall declining rate of anti-HBs was -42.39 mIU/mL per year. Participants with anti-HBs levels of >100-1000 mIU/mL at baseline had a faster decline rate than those with anti-HBs levels of 10-100 mIU/mL. Primary vaccination may not provide lifelong protection since HBV immunity deteriorates over time. Individuals with higher initial HBV immunity levels may experience a faster decline rate.
Keywords: healthcare workers; hepatitis B; primary vaccination; rate of immunity decline.