Male homosexuals are at risk for hepatitis A virus (HAV) infection, and HAV vaccination has been recommended to prevent HAV infection in male homosexuals. HIV infection may impair serological responses to HAV vaccination in HIV-infected patients. The investigators hypothesize that 3 doses of HAV vaccine will improve serological responses to HAV vaccine in HIV-infected patients.

In this study, we aim to compare the serological responses to HAV vaccination between HIV-infected patients who receive 2 doses or 3 doses of HAV vaccine and HIV-uninfected persons who receive 2 doses of HAV vaccine. Persons who identify themselves as male homosexuals aged younger than 40 years and are seronegative for hepatitis A virus will be enrolled. HAV vaccination will be provided free-of-charge. HIV-uninfected persons will receive 2 doses of HAV vaccine that will be administered at baseline and 6 months after the first dose, while HIV-infected patients will be given 2 doses or 3 doses of HAV vaccine; for those who choose to receive 3 doses, a second dose will be given 1 month after the first dose. A longitudinal follow-up of serological responses will be conducted to assess the effectiveness of HAV vaccination; HAV IgG will be determined at 6 months after the first dose of HAV vaccination(before the administration of the second dose), 12 months and 18 months after the first dose of HAV vaccination .

Inclusion Criteria:

• Age between 18~40-years-old
• Homosexuals

Exclusion Criteria:

• Presence of symptoms or signs suggestive of active infection
• Allergy to vaccination
• Failure to provide written informed consent
• Use of immunosuppressive or immunomodulating agents or chemotherapy