Prevention of Hepatitis A

Abstract

Hepatitis A virus (HAV) infection is a preventable, acute inflammatory disease of the liver caused by a member of the Picornavirus family. The HAV is a non-cytopatic, hepato-trophic RNA virus which replicates in hepatocytes and generates immune-mediated liver injury. Infection is mainly transmitted through fecal-oral route, close person-to-person contact, and intake of contaminated water or food. HAV endemicity is classified as high, intermediate, low, and very low, depending on age-adjusted prevalence of anti-HAV(IgG) antibodies in the population. The epidemiology and susceptibility to infection are driven by a number of factors including sanitary and socioeconomic conditions, age at exposure, and herd immunity. Improvement in socioeconomic conditions and in the level of hygienic standards in many countries with intermediate endemicity in transition has led to a shift in susceptibility to infection in adolescents and young adults. Major progress has been made in the past decades in prevention of hepatitis A. Pre- and postexposure prophylaxis using formaldehyde-inactivated HAV vaccines has gradually replaced the use of immune serum globulin for protection of subjects at risk. Live attenuated HAV vaccines have been developed in China for preexposure prophylaxis. Several attenuated HAV strains have been used for over 20 years in the United States, Europe, and China for manufacturing of formalin-inactivated vaccines. Administration of such highly immunogenic vaccines, given at two doses, separated by a flexible interval of 6–12 months, has had an excellent record of safety and tolerability. While most countries still employ a two-dose immunization strategy, Argentina and China chose to use a single-dose immunization strategy for UMV, using a formaldehyde-inactivated and live attenuated vaccine, respectively. Immunization strategies include universal mass vaccination (UMV) of toddlers, regional mass vaccination (RMV), and immunization of distinct risk groups. Introduction of UMV and RMV programs in the United States, Israel, several European countries, and in Australia has led to an unprecedented decline in the incidence of HAV infection and a rise in herd immunity in these regions.