Safety and immunogenicity of a pediatric formulation of inactivated hepatitis A vaccine in Argentinean children

Background. Children are a reservoir of hepatitis A virus and must be consi dered as primary targets of any immunization strategy. The safety and immun ogenicity were evaluated for a new formulation of an inactivated hepatitis A vaccine, Avaxim 80 units, containing one-half the antigen dose of the adu lt formulation. Methods. The safety of two doses of this vaccine given 6 months apart was e valuated in an open study in 537 Argentinean children 12 months to 15 Sears old. Immunogenicity was evaluated at Weeks 0, 2, 24 and 27 in a subgroup o f 120 subjects, Results. Two weeks after the first vaccine dose, >99% of initially seronega tive children had seroconverted (titers greater than or equal to 20 mIU/ml) , with a geometric mean titer of 98.5 mIU/ml, Before booster at 24 weeks al l subjects had seroconverted. A strong anamnestic response was observed aft er the second dose at which time the geometric mean titer had increased >35 -fold, and antibody titers were consistent with long term protection. Immed iate adverse reactions were observed in 3 of 537 (0.6%) subjects after the first dose. Local reactions were mild and transient and did not increase wi th subsequent doses. Among the systemic events reported during the 7-day fo llow-up period, 37 cases of fever after the first dose and 22 cases after t he second dose were reported. Only 3 cases of fever were clearly related to vaccination (less than or equal to 38.2 degreesC) after the first injectio n, all of which subsided in less than I day. Conclusions. This study demonstrated the safety and immunogenicity of a ped iatric formulation of hepatitis A vaccine in children ages 12 months to 15 years in healthy children ages 12 to 47 months.