Hepatitis A Prevention Through Immunization

by CDC

Summary

Routine vaccination of children is an effective way to reduce hepatitis A incidence in the United States. Since licensure of hepatitis A vaccine during 1995 - 1996, the hepatitis A childhood immunization strategy has been implemented incrementally, starting with the recommendation of the Advisory Committee on Immunization Practices (ACIP) in 1996 to vaccinate children living in communities with the highest disease rates and continuing in 1999 with ACIP's recommendations for vaccination of children living in states, counties, and communities with consistently elevated hepatitis A rates. These updated recommendations represent the final step in the childhood hepatitis A immunization strategy, routine hepatitis A vaccination of children nationwide. Implementation of these recommendations will reinforce existing vaccination programs, extend the benefits associated with hepatitis A vaccination to the rest of the country, and create the foundation for eventual consideration of elimination of indigenous hepatitis A virus transmission.

This report updates ACIP's 1999 recommendations concerning the prevention of hepatitis A through immunization and includes 1) new data on the epidemiology of hepatitis A in the era of hepatitis A vaccination of children in selected U.S. areas, 2) results of analyses of the economics of nationwide routine vaccination of children, and 3) recommendations for the routine vaccination of children in the United States. Previous recommendations for vaccination of persons in groups at increased risk for hepatitis A or its adverse consequences and recommendations regarding the use of immune globulin for protection against hepatitis A are unchanged from the 1999 recommendations.

Introduction

During 1980 - 1995, approximately 22,000 - 36,000 cases of hepatitis A were reported annually in the United States, representing an estimated average of 271,000 infections per year when anicteric disease and asymptomatic infections are taken in account. During 1995 - 1996, highly effective hepatitis A vaccines became available in the United States for use among persons aged >2 years, providing an opportunity to reduce hepatitis A incidence substantially and potentially eliminate indigenous transmission of hepatitis A virus (HAV).

In 1996, the Advisory Committee on Immunization Practices (ACIP) first made recommendations to prevent hepatitis A through immunization, focusing primarily on vaccinating persons in groups shown to be at high risk for infection and children living in communities with high rates of disease. In 1999, as the next step in a strategy of incremental implementation of recommendations for routine vaccination of children, ACIP expanded the recommendations to include vaccination of children living in states, counties, and communities in which hepatitis A rates were consistently above the national average. Coincident with implementation of these recommendations, hepatitis A rates have declined to the lowest level ever recorded. Because declines were largest in the areas in which routine vaccination of children was occurring, rates are now more equivalent across regions, with the highest rates occurring among children in parts of the country where vaccination has not been recommended. This statement includes recommendations for the final step in this incremental strategy, routine hepatitis A vaccination of children nationwide. Implementation of these recommendations will reinforce existing vaccination programs, extend the benefits associated with hepatitis A vaccination to the rest of the country, and create the foundation for eventual consideration of elimination of indigenous HAV transmission.

Clinical and Diagnostic Features of Hepatitis A

Clinical Illness

HAV, a 27-nm RNA agent classified as a picornavirus, can produce either asymptomatic or symptomatic infection in humans after an average incubation period of 28 days (range: 15 - 50 days). Illness caused by HAV infection typically has an abrupt onset that can include fever, malaise, anorexia, nausea, abdominal discomfort, dark urine, and jaundice. The likelihood of having symptoms with HAV infection is related to age. In children aged <6 years, 70% of infections are asymptomatic; if illness does occur, it is typically not accompanied by jaundice. Among older children and adults, infection typically is symptomatic, with jaundice occurring in >70% of patients. Signs and symptoms typically last <2 months, although 10% - 15% of symptomatic persons have prolonged or relapsing disease lasting up to 6 months. The overall case-fatality ratio among cases reported through the National Notifiable Diseases Surveillance System is approximately 0.3% - 0.6% but reaches 1.8% among adults aged >50 years; persons with chronic liver disease are at increased risk for acute liver failure.

In infected persons, HAV replicates in the liver, is excreted in bile, and is shed in stool. Peak infectivity of infected persons occurs during the 2-week period before onset of jaundice or elevation of liver enzymes, when concentration of virus in stool is highest. Concentration of virus in stool declines after jaundice appears. Children can shed HAV for longer periods than do adults, lasting up to 10 weeks after onset of clinical illness; infants infected as neonates in one nosocomial outbreak shed HAV for up to 6 months. Chronic shedding of HAV in feces does not occur; however, recurrent shedding occurs during relapses among persons who have relapsing illness. Viremia occurs soon after infection and persists through the period of liver enzyme elevation, but at concentrations several orders of magnitude lower than in stool.

About the Author

www.cdc.gov
The Centers for Disease Control and Prevention (CDC) is one of the 13 major operating components of the Department of Health and Human Services (HHS), which is the principal agency in the United States government for protecting the health and safety of all Americans and for providing essential human services, especially for those people who are least able to help themselves.