Persistence of antibody to Hepatitis A virus 20years after receipt of Hepatitis A vaccine in Alaska

Hepatitis A vaccine is recommended for children 1year old to prevent hepatitis A virus (HAV) infection. However, the duration of vaccine-induced immunity is unknown. We evaluated a cohort of Alaska Native persons 20years after HAV vaccination. Children aged 3-6years had been previously randomized to receive three doses of HAV vaccine (360 ELISA units/dose) at: (i) 0,1,2months; (ii) 0,1,6months; and (iii) 0,1,12months. We measured anti-HAV antibody concentrations every 2-3years; described geometric mean concentrations (GMC) and the proportion with protective antibody (20 mIU mL(-1)) over time; and modelled the change in GMC using fractional polynomial regression. Of the 144 participants, after 20years 52 (36.1%) were available for the follow-up (17, 18, 17 children in Groups A, B and C, respectively). Overall, 46 (88.5%) of 52 available participants had anti-HAV antibody concentrations 20 mIU mL(-1), and overall GMC was 107 mIU mL(-1). Although GMC levels were lower in Group A (60; CI 34-104) than in Group B (110; CI 68-177) or Group C (184; CI 98-345) (B vs C: P=.168; A vs B/C: P=.011), there was no difference between groups after adjusting for peak antibody levels post-vaccination (P=.579). Models predicted geometric mean concentrations of 124 mIU mL(-1) after 25years, and 106 mIU mL(-1) after 30years. HAV vaccine provides protective antibody levels 20years after childhood vaccination. Lower antibody levels in Group A may be explained by a lower initial peak response. Our results suggest a booster vaccine dose is unnecessary for at least 25-30years.