Long-term clinical observation of the immunogenicity of inactivated hepatitis A vaccine in children.

110 children who were given the complete course of the inactivated hepatitis A vaccine (Havrix) were followed up 10 years later. Age-matched healthy children who were not inoculated served as controls. One month after two primary injections, all children were positive for serum antibody. After 10 years, 99.09% of inoculated children remained positive for serum anti-HAV antibody, with a geometric mean concentration (GMC) of 61.59mIU/mL. GMC values following a secondary immunization in children with antibody levels <20mIU/mL were significantly elevated (567.9mIU/mL), compared with the primary injection alone. Havrix appears to induce persistent immunity and potent immune memory.