Comparison of the reactogenicity and immunogenicity of two different dose levels of inactivated hepatitis a vaccine in healthy children and adolescents

Poor hygiene, overcrowding and inadequate sanitation are the major environmental conditions for the most important route of trans­ mission of HAV, the fecal/oral route. In such conditions, the infec­ tion occurs early in life and is al­ most always subclinical. l Where standards of hygiene and sanitation are improved, there is a shift in epi­ demiology, with an increase in the average age of infection and a de­ crease in the prevalence of anti­ bodies against the virus. Changes in seroepidemiologic patterns of hepatitis A (HA V) in recent years are attributed to general improve­ ments in living standards. For the individual, active immunization can provide long-tenn protection against HAV infection; from a public health perspective, active immunization controls this disease effectively. Active immunization of children against hepatitis A became a reality in 1993, when the first pediatric hepatitis A vaccine was licensed. The initial schedule consisted of a two dose primary vaccination course with 360 ELISA Units SUMMARY An open study was performed to compare the reactogenicity and immunogenicity of an inactivated hepatitis A vaccine administered in two different doses and schedules to 460 healthy volunteers aged 3-18 years. PartiCipants were randomized to two groups to receive either two doses of 720 ELISA Units (EL.U) inactivated hepatitis A per 0.5 ml dose according to a 0,6-month schedule, or three doses of 360 EL.U according to a 0, 1, 6-month schedule. Transient local injection soreness was the most commonly reported symptom in almost half of both groups with no serious adverse events. One month after the primary course (one dose of 720 EL.U and two doses of 360 EL.U), 99% of 720 EL.U vaccinees had seroconverted, compared with 100% seroconversion in the 360 EL.U group. All vaccinees were seropositive after the booster dose of both vaccines with geometric mean anti-HAY titers of 2,359 and 2,967 miU/ml in the 720 EL.U and 360 EL.U groups, respectively. The vaccine containing 720 EL.U of antigen per dose offers the advantage of convenience and ac­ ceptance of immunization afforded by a two-dose course of vaccination accompanied by a comparable antibody response with that achieved after three doses of vaccine containing 360 EL.U of antigen per dose.