Abstract
Infection with hepatitis A virus (HAV) is common in children. Among children < 5 years of age, < 10% present with jaundice and manifest HAV infection with diarrhea, nausea, vomiting, malaise or no visible signs or symptoms. Prior to introduction of hepatitis A vaccine in the United States, the reported incidence of symptomatic disease was highest among children 5 to 14 years of age (15.6/100,000), however, seroprevalence data indicated that children < 5 years of age had the highest infection incidence (637.4/100,000). The significance of these finding is that young children with asymptomatic infection act as silent reservoirs for HAV transmission within the community. Hepatitis A immunization provides long-term immunity against HAV infection and early childhood immunization has been shown to halt HAV transmission in communities with previously high incidence of disease. Incorporation of hepatitis A vaccine into the early childhood immunization schedule was impeded by the finding that passively acquired maternal antibody significantly inhibited immunogenicity of vaccine administered during infancy. However, recent studies have shown that little passively acquired antibody remains early in the second year of life and does not interfere with vaccine immunogenicity. Early childhood hepatitis A vaccination has significantly lowered disease incidence in a number of populations, worldwide. Among vaccinated and unvaccinated children, there has been a > 85% reduction in disease incidence and a 69-90% reduction in disease incidence among unvaccinated adults in the same populations. The effectiveness and costeffectiveness of childhood hepatitis A vaccination combined with no increase in adverse events among more than 2.3 million vaccinated children has led to recent recommendations that hepatitis A vaccine be incorporated into the early childhood immunization schedule in the United States.
Keywords: hepatitis A virus (HAV) transmission, immunization, Vaccination, Disease Control and Prevention (CDC), Antibody
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