This study will assess the efficacy of a new intradermal formulation of the trivalent inactivated influenza vaccine compared to the standard intramuscular vaccine in HIV-infected men who have sex with men in Bangkok, Thailand. Relative efficacy of the two different formulations of influenza vaccine will be assessed by comparing immunologic responses to vaccine between the two study arms.

This study will assess the efficacy of a new intradermal formulation of the trivalent inactivated influenza vaccine (TIV) compared to standard intramuscular TIV in HIV-infected men who have sex with men (MSM) in Bangkok, Thailand. Eligible participants will be randomized to receive standard full-dose intramuscular vaccine versus full-dose intradermal vaccine. Full dose (15 micrograms) intradermal TIV will be licensed for use in adult's ≥ 60 years of age in Thailand in mid-2011. In this study, intradermal TIV will be used off-label as the 15 microgram dose will be administered to individuals < 60 years of age. Efficacy of the two different formulations of influenza vaccine will be assessed by comparing immunologic responses to vaccine between the two HIV-infected study arms. Both humoral (influenza antibody) and cell-mediated (influenza- specific CD4 and CD8 T cell) immune responses will be evaluated. Humoral and cell-mediated immune responses among HIV-infected individuals with CD4 cell counts less than 200 per microliter will also be compared to immune responses in HIV-infected individuals with CD4 cell counts of 200 per microliter or greater. A small HIV-uninfected MSM control group will also be enrolled (with persons randomized into either an intramuscular or intradermal TIV arm) to serve as a comparator group for the cell-mediated immunity studies.

Inclusion Criteria:

• Thai men by nationality who have sex with men
• HIV-infected or HIV-uninfected men
• At least 18 years of age
• Willing and able to provide written informed consent
• Availability and commitment for 12 months of study follow-up (3 study visits)

Exclusion Criteria:

• Men with severe allergies to chicken eggs (they will specifically be asked about severe egg allergies during the screening visit; appendix C1)
• Men > 60 years of age
• Men who have had a severe reaction to influenza vaccine in the past
• Men with a history of Guillain-Barré Syndrome
• Men who received influenza vaccine within 12 months prior to enrollment
• Men who are on steroid therapy or other immunosuppressant medications
• Men who received any vaccine in the 4 weeks prior to the first study visit or who plan to receive a vaccine (other than influenza vaccine provided through the study protocol) in the 4 weeks following the first study visit
• Men who received an experimental agent (vaccine, drug, biologic, device, blood product, medication) within 1 month prior to enrollment in this study, or expect to receive an experimental agent during the 12 month study period
• Men who have any condition, in the opinion of the investigator, that would place them at an unacceptable risk of injury or render them unable to meet requirements of the protocol. (e.g., severe reaction to another vaccine, blood clotting disorder, inflammatory skin condition).
• Foreign (non-Thai) nationality