Duration of Long-term Immunity After Hepatitis B Virus Immunization

Background: * The hepatitis B vaccine has been shown to be safe and effective in preventing transmission of the hepatitis B virus. Response rates to the initial three doses of the vaccine are high, with significant or even complete immune response. However, this level has been reported to decline rapidly within the first year and more slowly thereafter. There is little data on the durability and long-term protection provided by the hepatitis B vaccine administered to adults in the United States. * Vaccinated individuals are believed to be protected against hepatitis B virus infection because of a memory immune response. Even if antibody levels are low, the immune system will still be able to produce enough antibody to neutralize the hepatitis B virus. Therefore, booster doses of the vaccine are not recommended, except for some high-risk individuals such as patients on dialysis. Researchers are interested in determining the durability of the immune response of the hepatitis B vaccine in adults with low or intermediate risk for hepatitis B virus infection. Objectives: \- To examine the long-term immune status of human immunodeficiency virus (HIV) positive and negative individuals who received the hepatitis B vaccine during adulthood, compared with the immune status of individuals who acquired natural immunity by recovering from acute hepatitis B during adulthood. Eligibility: * Individuals at least 18 years of age who were vaccinated against hepatitis B at least 10 years ago. * Individuals at least 18 years of age who contracted and recovered from acute hepatitis B at least 10 years ago. * Individuals at least 18 years of age who have well-controlled HIV and were vaccinated against hepatitis B at least 10 years ago. Design: * Participants will have a single outpatient study visit and potential follow-up visits as part of this protocol. * Participants will complete a questionnaire assessing possible risk factors for hepatitis B infection, and will provide blood