Reference:
Update: Prevention of Hepatitis A after Exposure to Hepatitis A Virus and in International Travelers (MMWR 10/19/07, Vol. 56, No. 41) available at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5641a3.htm. Updated Recommendation of the Advisory Committee on Immunization Practices (ACIP).

When administered within 2 weeks of exposure, immune globulin (IG) is 80%-90% effective in preventing clinical hepatitis A and hepatitis A vaccine has comparable efficacy. Persons who have been administered at least one dose of hepatitis A vaccine at least 1 month before exposure to hepatitis A virus (HAV) do not need postexposure prophylaxis.

Persons who have been recently exposed (see exposure groups below) to hepatitis A virus and who have not previously been administered hepatitis A vaccine should be administered a single dose of single-antigen hepatitis A vaccine or immune globulin (IG, 0.02 mL/kg) as soon as possible, but not >2 weeks after the most recent exposure.

• For healthy persons aged 12 months-40 years, single-antigen hepatitis A vaccine at the age-appropriate dose is preferred.
• For persons aged >40 years, IG is preferred; vaccine can be used if IG cannot be obtained.
• For children <12 months, immunocompromised persons, persons who have chronic liver disease, and persons for whom vaccine is contraindicated, IG should be used.

Because hepatitis A cannot be reliably diagnosed on clinical presentation alone, serologic confirmation of HAV infection in index patients by IgM anti-HAV testing is recommended before postexposure prophylaxis of contacts. Screening of contacts for immunity before giving postexposure prophylaxis is not recommended because screening is more costly and would delay its administration. If hepatitis A vaccine is recommended for a person being given IG, it may be administered simultaneously with IG at a separate anatomic injection site. For persons who receive hepatitis A vaccine, the second dose should be administered according to the licensed schedule of the product.

Postexposure prophylaxis (PEP) should be administered to previously unvaccinated persons in the following situations:

• Close personal contact:
  Postexposure prophylaxis should be administered to all unvaccinated household and sexual contacts of persons who have hepatitis serologically confirmed (hepatitis IgM anti-HAV positive) as hepatitis A. PEP should also be administered to unvaccinated persons who have shared illicit drugs with a person with serologically confirmed acute hepatitis A, and should be considered for unvaccinated persons with ongoing close personal contact (e.g., regular babysitting) with a person with hepatitis due hepatitis A virus infection.
• Day care centers:
  In day care centers or homes where children who wear diapers are cared for, PEP should be administered to all previously unvaccinated staff and attendees if a) one or more cases of hepatitis A are recognized in children or employees or b) cases are recognized in two or more households of center attendees. In centers that do not provide care to children who wear diapers, PEP need be given only to unvaccinated classroom contacts of an index case-patient. When an outbreak occurs (i.e., hepatitis cases in three or more families), PEP also should be considered for unvaccinated members of households that have children (center attendees) in diapers.
• Common-source exposure:
  If a food handler is diagnosed with hepatitis A, PEP should be administered to other food handlers at the same location. Because common-source transmission to patrons is unlikely, PEP for patrons is usually not recommended but may be considered if a) during the time when the food handler was likely to be infectious, the food handler both directly handled uncooked foods or foods after cooking and had diarrhea or poor hygienic practices and b) patrons can be identified and treated within 2 weeks after the exposure. In settings where repeated exposures to HAV may have occurred (e.g., institutional cafeterias), stronger consideration of PEP for patrons may be warranted. In the event of a common-source outbreak, PEP should not be administered to exposed persons after cases have begun to occur because the 2-week period during which PEP is known to be effective will have been exceeded.
• Schools, hospitals, and work settings:
  PEP is not routinely indicated when a single case occurs in an elementary or secondary school, an office, or in other work settings, and the source of infection is outside the school or work setting. Similarly, when a person who has hepatitis A is admitted to a hospital, staff should not routinely be administered PEP; instead, careful hygienic practices should be emphasized. PEP should be administered to persons who have close contact with index patients if an epidemiologic investigation indicates HAV transmission has occurred among students in a school or among patients or between patients and staff in a hospital.