Hepatitis A: from epidemic jaundice to a vaccine-preventable disease

Hepatitis A probably causes an identifiable illness in less than 5% of individuals who are infected with the virus. Nonetheless, it has been an important cause of morbidity throughout history. Hepatitis A remains endemic in some developing nations, and cyclical epidemics still occur in developed nations, including the United States. Because infections are less common in children in developed nations, the pattern of infection has shifted toward older age groups. This shift is a concern because the disease tends to be far more symptomatic in older patients, and more than 70% of reported deaths are among persons older than 49 years of age. Hepatitis A does not cause chronic disease, but atypical presentations associated with a relapse may persist for several months. Although the risk of infection can be significantly reduced by adhering to good sanitary precautions, these precautions are not always practiced in certain environments, and there is a need for a universal immunization strategy. Passive immunization with pooled immune serum globulin is effective when administered within 2 to 3 weeks of exposure. Unfortunately, the window of opportunity is often missed because the majority of cases of hepatitis A have no history of exposure. The effectiveness of immune serum globulin is also short-lived. An effective breakthrough in prevention occurred with the development of a killed vaccine, which has proven to be effective for active immunization. It was licensed in the United States in 1995.