07-26-2010, 06:09 PM
Infection with HAV induces lifelong immunity. In areas of low endemicity, hepatitis A usually occurs as single cases among persons in high-risk groups or as outbreaks involving a small number of persons. In areas of high endemicity most persons are infected with HAV without symptoms during childhood. This explains why clinical hepatitis A is uncommon. In countries of low and intermediate disease endemicity, adult disease is seen more often. Hepatitis A may represent a substantial medical and economic burden. Currently, four inactivated vaccines against HAV are internationally available. All four vaccines are safe and effective, with long-lasting protection. None of the vaccines are licensed for children less than one year of age.
Protective antibodies develop in response to infection and persist for life. The protective role of anti-HAV antibodies has been demonstrated by the protection against hepatitis A resulting from passive immunization with serum immune globulin. The effect of mucosal immunity on HAV infection is not known.
reference:http://www.who.int/vaccines/en/hepatitisa.shtml
Protective antibodies develop in response to infection and persist for life. The protective role of anti-HAV antibodies has been demonstrated by the protection against hepatitis A resulting from passive immunization with serum immune globulin. The effect of mucosal immunity on HAV infection is not known.
reference:http://www.who.int/vaccines/en/hepatitisa.shtml