Long-term antibody persistence in children after vaccination with the pediatric formulation of an aluminum-free virosomal hepatitis A vaccine

Background: The pediatric dose of the virosomal hepatitis A vaccine Epaxal (R), Epaxal (R) Junior, is safe and immunogenic in children from 1 to 17 years of age. The present study investigated the long-term immunogenicity of Epaxal (R) Junior. The standard doses of Epaxal (R) and aluminum-adsorbed hepatitis A vaccine (Havrix (R) Junior) were used as comparators. Methods: A total of 271 children who had completed a 0/6-month immunization schedule (priming and booster dose) participated in this follow-up study. Anti-hepatitis A virus (HAV) antibody levels were measured using a microparticle enzyme immunoassay (HAVAB 2.0 Quantitative; Abbott Diagnostics, Wiesbaden, Germany) starting at 18 months following the second dose, and then yearly until 66 months (ie, 5.5 years) after the second dose. Results: All subjects tested at Month 66 still had protective anti-HAV antibodies (>= 10 mIU/mL). Antibody titers were generally lower in subjects 1-7 years old than in subjects 8-17 years old and higher in females 11-17 years old than in males 11-17 years old. In addition, an age-dependent decay was observed, that is, antibody decreased more rapidly in younger than in older children. Conclusions: Vaccination of children with two doses of Epaxal (R) Junior confers a real-time protection of at least 5.5 years. This protection is estimated to last approximately 25 years. Younger children showed lower antibody titers and a faster antibody decline than older children. Additional follow-up studies are needed beyond 5.5 years to further assess the longterm immunogenicity of Epaxal (R) Junior.