FOLLOW-UP IMMUNOGENICITY OF AN INACTIVATED HEPATITIS-A VIRUS-VACCINE IN HEALTHY-CHILDREN - RESULTS AFTER 5 YEARS

Long-term persistence of hepatitis A virus (HAV) serum antibody in vac cinated children has not been demonstrated in previous studies. To stu dy the long-term immunogenicity to HAV vaccine, three doses of strain HM 175 HAV vaccine with 360 enzyme-linked immunosorbent assay units we re administered to 107 children, aged from 1.0 to 6.8 years, at 0, 1, and 6 months. The administration of one vaccine nose induced seroposit ivity (anti-HAV titer greater than or equal to 20 mlU ml(-1)) in 95% o f all vaccinees at month 1. All subjects remained seropositive until m onth 6. The titers of HAV antibody remained above 20 mlU ml(-1) in all subjects followed up to 60 months. The geometric mean titer (GMT) rea ched its peak (3802 mlU ml(-1)) at month 7, i.e. 1 month after the boo ster dose, and then declined until the end of follow-up at month 60 (6 61 mlU ml(-1)). A trend of higher GMT in female subjects persisted Lip to month 60. The changes of the GMT over time were best described by the regression equation: log (GMT) = 3.26-0.08 x (age in years) (r = - 0.95, P = 0.014). According to this equation, the geometric mean conce ntration would reach 20 mlU ml(-1) at around 24.5 years after the begi nning of vaccination. In conclusion those who completed the recommende d three-dose inactivated HAV vaccination series remained seroprotectiv e for at least 5 years. Theoretically such a vaccination program can p rovide a protective period of over 20 years in children. This paper ma y be the first to describe at least 5-year immunogenicity of inactivat ed HAV vaccination in healthy children. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.