甲型肝炎一般是良性的感染,但亦可能迁延或复发,偶致暴发性肝衰竭。发病随年龄增长而变严重。在卫生不良的国家,幼儿普遍受染,很少发病,但获终生免疫。随着卫生情况改善,感染推迟发生,使青少年或成年人出现有临床表现的甲型肝炎。疾病多见于年龄稍大的人的这种变化,是致力于寻找疫苗的因素之一。在发达国家免疫率与年龄相关,而且免疫 Hepatitis A is generally a benign infection, but it may also delay or relapse and cause fulminant fulminant hepatic failure. The incidence increases with age and become serious. In poorly-sanitized countries, young children are commonly infected, rarely ill but immunized for life. As the health situation improves, infection is postponed, giving rise to clinical manifestations of hepatitis A in adolescents or adults. This change, which is more common in older people, is one of the factors driving the search for vaccines. Immune rates in developed countries are age-related and immune