Hepatitis A, caused by infection with the Hepatitis A virus (HAV), has an incubation period of approximately 28 days (range: 15 to 50 days). HAV replicates in the liver and is shed in high concentrations in feces from 2 weeks before to 1 week after the onset of clinical illness. HAV infection produces a self-limited disease that does not result in chronic infection or chronic liver disease.

However, 10 to 15% of patients might experience a relapse of symptoms during the 6 months after the acute illness. Acute liver failure from Hepatitis A is rare (overall case-fatality rate: 0.5%). The risk for symptomatic infection is directly related to age, with more than 80% of adults having symptoms compatible with acute viral hepatitis while the majority of children are either asymptomatic or have unrecognized infection. Antibody produced in response to HAV infection persists for life, and confers protection against reinfection.

HAV infection is primarily transmitted by the fecal-oral route, either by person-to-person contact or through consumption of contaminated food or water. Although viremia occurs early in infection and can persist for several weeks after onset of symptoms, bloodborne transmission of HAV is uncommon.

In the United States, nearly half of all reported Hepatitis A cases have no specific risk factor identified. Among adults with identified risk factors, the majority of cases are among men who have sex men (MSM), persons who use illegal drugs, and international travelers.

Because transmission of HAV during sexual activity probably occurs because of fecal-oral contact, measures typically used to prevent the transmission of other sexually transmitted diseases (STDs), such as use of condoms, do not prevent HAV transmission. In addition, efforts to promote good personal hygiene generally have not been successful in interrupting outbreaks of Hepatitis A. Vaccination is the most effective means of preventing HAV transmission among persons at risk for infection. Hepatitis A vaccination is recommended for all children at 1 year of age, for persons who are at increased risk for infection (e.g., men who have sex with men), for persons who are at increased risk for complications from Hepatitis A, and for any person wishing to obtain immunity.

Hepatitis A vaccine is considered the best protection against contracting the virus. More than 95 percent of adults will develop a protective antibody response within four weeks of a single dose of vaccine, and nearly 100 percent will develop a protective antibody response after receiving two doses. Among children and adolescents, more than 97 percent will develop a protective antibody response within a month of the first dose. In clinical trials, all recipients had protective levels of antibody after two doses.

Vaccine is recommended for the following persons, 12 months of age and older, who are most at risk of becoming infected with HAV:

• Persons working or who are traveling in countries where they have a high or intermediate risk of hepatitis A infection. These areas include all areas of the world except Canada, Western Europe and Scandinavia, Japan, New Zealand, and Australia.
• Contacts (including household and sexual contacts) of infected persons
• Men who have sex with men
• Persons who use illegal drugs
• Persons who have clotting disorders

Hepatitis A vaccination is not routinely recommended for healthcare workers, persons attending or working in child care centers, or persons who work in liquid or solid waste management (e.g., sewer workers or plumbers). These groups have not been shown to be at increased risk for hepatitis A.