Immunogenicity and safety of two doses of a paediatric hepatitis A vaccine in thai children: comparison of three vaccination schedules.

As fewer children in Thailand are exposed to hepatitis A virus (HAV) and so do not have seroprotective anti-HAV antibodies, they are becoming an important source of HAV transmission. A flexible HAV vaccination schedule would facilitate incorporation of the vaccine into existing immunization programmes, and we compared the immunogenicity and safety of three HAV immunization schedules. An open, randomized, clinical trial was carried out in which healthy children were given a primary dose of the inactivated hepatitis A vaccine, Avaxim 80 paediatric, with a booster dose 6, 12 or 18 months later. Anti-HAV geometric mean concentrations (GMC), seroconversion rates, and GMC ratios (GMCR) of the three schedules were compared and reactogenicity was evaluated. Seroconversion rates were above 98 per cent (per group) up to the booster. The three schedules were equivalent in terms of GMCRs, each eliciting a large booster effect. Local reactions were reported for fewer than 9 per cent of each group after dose one and less frequently after the booster dose. Injection site pain, gastrointestinal tract disorders and fever were the most commonly reported adverse events. No vaccine-related serious adverse events were reported. It was concluded that the hepatitis A vaccine, Avaxim 80 paediatric, is safe and immunogenic when given as a two-dose schedule to healthy seronegative children aged 5-10 years, with the second dose given at either 6, 12 or 18 months after the first.