Prevention of Hepatitis A Through Active or Passive Immunization

Rationale For Prevention of Hepatitis A Through Active Immunization

In the United States during the past several decades, a decline in the overall incidence of hepatitis A has occurred primarily as a result of better hygienic and sanitary conditions (e.g., improved water supplies, sewage disposal, and food sanitation and less crowded living conditions). Although passive immunization with IG has been available for several decades, its effect on lowering the incidence of hepatitis A has been limited. High rates of disease among many segments of the U.S. population and the continued occurrence of extensive communitywide outbreaks indicate that hepatitis A remains a major public health problem.

The availability of hepatitis A vaccine provides an opportunity to substantially lower disease incidence and eventually eradicate infection. This reduction in disease incidence will be achieved by producing high levels of immunity in persons in age groups that have the highest rates of HAV infection and that serve as a reservoir of infection ⁽²⁶⁾. Producing a highly immune population decreases the incidence of hepatitis A and presumably decreases virus circulation by preventing fecal shedding of HAV. Populations are highly immune following an epidemic in communities that have high rates of hepatitis A or following vaccination in such communities ⁽²⁹⁾. Hepatitis A immunization is likely to substantially lower disease incidence because HAV does not produce a chronic infection, and humans are the only natural reservoir of the virus.

Because of their critical role in HAV transmission, children should be a primary focus of immunization strategies to lower disease incidence. Thus, the most effective means of achieving control of HAV infection would be to include routine hepatitis A vaccination in the childhood vaccination schedule. However, the lack of data available for determining the appropriate dose and timing of vaccination in the first or second year of life presents a barrier to the implementation of this strategy. Combination vaccines that include inactivated HAV would minimize the number of injections administered to children.

Until hepatitis A vaccine is licensed for use among children <2 years of age, the interim strategy to prevent and control hepatitis A should focus on preexposure vaccination of the following persons: a) persons at increased risk for HAV infection or its consequences (e.g., travelers and persons who have chronic liver disease); b) children living in communities that have high rates of hepatitis A to help prevent recurrent epidemics; and, if indicated, c) children and young adults in communities that have intermediate rates of hepatitis A to help control ongoing and prevent future epidemics. In addition, contacts of case-patients should be administered postexposure prophylaxis (i.e., IG or, when appropriate, IG and hepatitis A vaccine).

Vaccination of persons in groups at increased risk for HAV infection (e.g., travelers) will likely have little effect on national disease rates because most cases do not occur among persons in these groups. Vaccination of persons in communities with high and intermediate rates of disease might have an impact on national disease incidence.

However, a substantial reduction in the incidence of disease cannot be expected until hepatitis A vaccine is included in the routine childhood immunization schedule and successive cohorts of children are vaccinated.