Long-term immunogenicity of inactivated hepatitis A vaccine: Follow-up at 15 years

Abstract

We conducted a 10-15 years follow-up to a long-term prospective cohort study on the immunogenicity of inactivated hepatitis A vaccine in Alaska Native children, who were initially vaccinated between 3-6 years of age. Children received three vaccine doses (320 E.U.) and were randomized into the following vaccination schedules: A (0, 1, 2 months); B (0, 1, 6 months); and C (0, 1, 12 months). Sera were collected every 2 years and tested for hepatitis A virus (anti-HAV). Levels 20 mIU/mL were considered protective. Anti-HAV geometric mean concentrations were compared by vaccination schedule at 10, 12 and 14 years of follow-up, using ANOVA. Antibody decline over the entire 15-year follow-up period was also analyzed. While none of the inter-schedule comparisons differed significantly from each other at the 10, 12 and 14-year periods, schedules B and C had significantly higher anti-HAV levels than schedule A over the entire 15 years of the study ( P< 0.01). All schedule B and C children maintained seroprotective levels in all follow-up periods. Fourteen percent of schedule A children fell below seroprotective levels at 14 years. Our model estimated that anti-HAV geometric mean concentrations would fall below seroprotective levels at 26, 30 and 32 years for schedules A, B and C, respectively. The data indicate that hepatitis A immunity lasts at least 15 years after vaccination in children and that a booster dose is not needed during that time. However, continued monitoring is necessary to assess the need for a booster dose later in the second and third decade after receipt of the primary series.