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Response to Hepatitis A Vaccine in Children after a Single Dose with a Booster Administration 6 Months Later.

Background: Children are of an age group susceptible to infection by the hepatitis A virus (HAV). Active immunization of children against HAV became reality in 1993, when the first pediatric hepatitis A vaccine was licensed. This initial vaccine required two injections to induce a full immune response in recipients. The purpose of this study was to assess the feasibility of a single dose primary vaccine plus a booster after 6 months against hepatitis A in children. Methods: A total of 60 healthy and seronegative children between 2 and 13 years of age were administered inactivated hepatitis A vaccine, containing 720 enzyme-linked immunosorbent assay (ELISA) units (EL.U) of hepatitis A antigen, intramuscularly in the deltoid region at months 0 and 6. Symptoms were recorded by parents or guardians on individual diary cards. Antibodies against HAV (antiHAV) were measured using an ELISA inhibition assay, and a seropositive titer was defined as being >=20 mIU/mL. Results: Fifteen days after the single primary dose, 96% of the vaccinees were seropositive with a geometric mean titer (GMT) of 351 mIU/mL. The seropositivity rate reached 100% 1 month after the first dose, with a GMT of 305 mIU/mL. Prior to the second dose at month 6, 93% remained seropositive, and the GMT was 153 mIU/mL. By month 7, 1 month after the second vaccination, the seropositivity rate recovered to 100% with a rise in GMTs to 3644 mIU/mL. Local symptoms were reported after 23.9% of doses, and general symptoms after 19.7% of doses. All symptoms were of short duration and resolved spontaneously. Conclusions: This inactivated vaccine against hepatitis A is safe, well-tolerated, and excellently immunogenic when administered to children following a single dose plus booster course at months 0 and 6.