General Approach Following Exposure to Hepatitis A Virus
Transmission of hepatitis A virus (HAV) results primarily via the fecal-oral route, through either person-to-person contact or by ingestion of contaminated food or water. The evaluation and management of a patient potentially exposed to HAV entails a three-part strategy. First, the context in which the exposure occurred should be considered, and need for administering postexposure prophylaxis assessed. Second, if this assessment reveals that the exposure warrants postexposure prophylaxis, immune globulin (IG) should be administered. Third, assessment of future risk for acquisition of hepatitis A virus (HAV) should direct administration of hepatitis A vaccine to prevent future infection.
Assessment for Hepatitis A Postexposure Prophylaxis
Administering postexposure prophylaxis to prevent hepatitis A should occur if the following four criteria are met.
Recommendations for Postexposure Prophylaxis
Historically, only IG was recommended for HAV postexposure prophylaxis, whereas HAV vaccine was recommended primarily for pre-exposure prophylaxis. In October 2007, the US Advisory Committee on Immunization Practices (ACIP) updated their guidelines to include HAV vaccine in the postexposure prophylaxis recommendations. The revision in the ACIP guidelines was based on results of a randomized, double-blind non-inferiority trial that demonstrated comparable efficacy of HAV vaccine and IG when administered within 14 days of exposure to HAV in healthy persons 12 months to 40 years of age. Assuming IG is 90% efficacious in preventing HAV, the vaccine was estimated to have 86% efficacy in preventing symptomatic HAV infection (95% CI 73-93%). The vaccine has a number of advantages for postexposure prophylaxis when compared with IG, including induction of active immunity that provides long-term protection, greater ease of administration, higher patient acceptability, and widespread availability. Screening of the exposed individual for HAV immunity by measuring serum antibody to HAV before administering HAV vaccine or IG is not recommended for two reasons. First, serologic screening is generally not cost effective in this setting. Second, waiting for the results of screening can delay vaccine or IG administration and thus reduce the efficacy of postexposure prophylaxis.
2007 ACIP Recommendations for Postexposure Prophylaxis
The 2007 ACIP postexposure prophylaxis recommendations state that persons recently exposed to hepatitis A and who have not previously received HAV vaccination should be administered either a single-dose of HAV single-antigen vaccine or immune globulin (IG) as soon as possible, and within 14 days after exposure. No information exists regarding the efficacy of IG or vaccine if administered >2 weeks after exposure. These guidelines, however, stratify the recommendations based on the patient population exposed:
For groups other than healthy persons 12 months-40 years of age, the ACIP recommendation to use IG takes into account the lack of data on vaccine performance in these groups, as well as the greater risk of severe consequences of HAV among older patients and patients with chronic liver disease. Persons who receive HAV vaccine for postexposure prophylaxis should receive the second dose at the appropriate licensed schedule to complete the series. In addition, for persons receiving IG postexposure prophylaxis and for whom HAV vaccine is recommended for long-term HAV protection, the first dose of the HAV vaccine series should be given at the same time the IG is given, though in a separate anatomic site.
Administering HAV Vaccine for Postexposure Prophylaxis
When using HAV vaccine in the postexposure prophylaxis setting, any of the single antigen licensed HAV vaccines can be used, but the vaccine series should be given at the age-appropriate schedule and dose (Figure 2). Hepatitis A vaccine should be administered as an intramuscular dose in the deltoid muscle. Two inactivated hepatitis A vaccines are available in the United States (Havrix and Vaqta). The updated recommendations for use of hepatitis A vaccine alone for postexposure prophylaxis do not apply to the combination hepatitis A/hepatitis B vaccine (Twinrix) because no data exist regarding the performance of the combination vaccine for prophylaxis after exposure to HAV. The concentration of HAV antigen in the currently available combination vaccine formulation is half that included in the single-antigen vaccine available from the same manufacturer.
Administering Immune Globulin (IG) for Postexposure Prophylaxis
When IG is administered, it should be given as a a single intramuscular dose (0.02 mL/kg) in the deltoid or gluteal muscle, as these sites can accommodate a large volume injection with a needle length appropriate for the person's age and size. If administered within 2 weeks following an exposure to HAV, IG is more than 85% effective in preventing hepatitis A [1,2]. Efficacy is greatest when IG is administered early in the incubation period. Hepatitis A vaccine and IG can be administered simultaneously, but they should be given at separate anatomic injection sites. In general, IG does not interfere with the immune response to inactivated vaccines; it can, however, interfere with the response to many live, attenuated vaccines, and appropriate precautions should be taken to have a sufficient interval between IG administration and certain live vaccines [1,2]. Although IG is made from pooled human plasma, the preparation of IG includes multiple steps to ensure the final product does not contain any potentially infectious pathogens. Indeed, no instances of transmission of HIV, hepatitis B virus, hepatitis C virus, or other viruses have been reported with the intramuscular use of IG. In addition, pregnant women and women who are nursing can safely receive IG.
Completing Hepatitis A Vaccine Series for Long-Term Protection
As noted, persons receiving hepatitis A vaccine for postexposure prophylaxis should complete the hepatitis A vaccine series to provide long-term protection against HAV infection. In addition, individuals who receive IG for postexposure prophylaxis and for whom hepatitis A vaccine is also recommended (for other reasons) should receive the hepatitis A vaccine series. Further details regarding hepatitis A vaccine, including indications for routine preexposure prophylaxis, are provided in the Hepatitis A Vaccine case in this same Hepatitis A module. Postvaccination testing to determine adequate immune response is not indicated since the vaccine series induces protective antibody levels in greater than 99% of healthy adults.