Long-term Serologic Follow-up of Children Vaccinated with a Pediatric Formulation of Virosomal Hepatitis A Vaccine Administered With Routine Childhood Vaccines at 12-15 Months of Age.

ABSTRACT

BACKGROUND: The aim of this open-label, active-controlled, parallel group, phase 2 follow-up study was to assess the long-term immunogenicity of Epaxal Junior, the pediatric dose of an aluminum-free virosomal inactivated hepatitis A virus (HAV) vaccine, in children receiving routine childhood vaccines (RCV). METHODS: Healthy children (12-15 months old, ≥8 kg weight) were randomized (111) to group A Epaxal Junior + RCV (day 1); group B Epaxal Junior (day 1) + RCV (day 29) and group C Havrix 720 + RCV (day 1). All 3 groups received 2 doses of HAV vaccines 6 months apart. Children who completed the primary study were followed up from 18 months to 7.5 years post booster. RESULTS: Of 291/327 randomized children who had completed the primary study, 157 were followed for the 7.5-year analysis (group A 50; group B 54; and group C 53). Of these, 152 children had protective levels of anti-HAV antibodies [≥10 mIU/mL; 98% (group A); 96.3% (group B); 96.2% (group C)]. Anti-HAV geometric mean concentrations were similar in groups A and B at all the time points (1.5-, 2.5-, 3.5-, 5.25- and 7.5-year time point) but slightly lower in group C. Predictions of the median duration of persistence of seroprotective antibody levels, using the linear mixed model were similar in all groups (group A 19.1 years, group B 18.7 years, group C 17.3 years). CONCLUSIONS: Immunization with Epaxal Junior administered with RCVs at 12 months elicited protective response beyond 7.5 years in almost all children. Assessing the kinetic of anti-HAV antibody titers decline over time, the moment to reach antibody concentrations below the accepted protective level may occur earlier than previously estimated.