Patient description: A 67-year-old healthy woman came to the clinic to have her flu shot in early October. She works at a rehab center and has no underlying disease. It is her first vaccination this year. she is menopausal and has 4 children. She does not some. She takes daily multivitamins and anti-hypertensive drugs. She exercises regularly for 30 minutes a day at least 5 days a week. She has no allergies to any food or drugs.

Clinical trial eligibility criteria: eligible ages (years): 0.0-999.0,  HIV Infections HIV Positive: 1. Age greater than or equal 18 but less than or equal to 60 years old and willing and able to give informed consent 2. Enrollment during the USA influenza season (October-March) 3. Self-reported history of HIV infection at enrollment (If NIH HIV testing does not confirm that the subject is HIV-positive, the subject will be discontinued from the study and not included in the analysis.) HIV Negative: 1. Age greater than or equal to 18 but less than or equal to 60 years old and willing and able to give informed consent 2. Enrollment during USA influenza season (October-March) 3. Self-reported healthy HIV-negative (If NIH HIV testing does not confirm that the subject is HIV-negative, the subject will be discontinued from the study and not included in the analysis.)  HIV Positive: 1. Self-reported history of vaccination with the trivalent influenza preparation used for the current influenza season 2. Self-reported vaccination with any vaccine within the one month period prior to study enrollment 3. Acute febrile illness (may defer vaccine until resolved) 4. History of hypersensitivity to any influenza vaccine components including thimerosal or egg 5. History of Guillain-Barre syndrome 6. Intention to receive any other vaccine during the study period 7. Pregnancy 8. Self-reported treatment with immunomodulator/immunosuppressive drugs (interleukins, corticosteroids, or G(M)-CSF in the 4 weeks prior to enrollment 9. Self-reported history of IL-2 administration within the past 5 years 10. Use of theophylline preparations or warfarin because of the theoretical possibilities, of enhanced drug effects and toxicities post influenza vaccination 11. Active infection or other serious illness other than HIV that might affect the immune response to a vaccine 12. Current alcohol, substance abuse, or systemic/psychiatric illness that potentially could interfere with patient compliance and ability to make study visits HIV Negative: 1. Self-reported history of vaccination with the trivalent influenza preparation used for the current influenza season 2. Self-reported vaccination with any vaccine within the one month period prior to study enrollment 3. Acute febrile illness (may defer vaccine until resolved) 4. History of hypersensitivity to any influenza vaccine components including thimerosal or egg 5. History of Guillain-Barre syndrome 6. Intention to receive any other vaccine during the study period 7. Pregnancy 8. Self-reported treatment with immunomodulator/immunosuppressive drugs (interleukins, corticosteroids, or G(M)-CSF in the 4 weeks prior to enrollment 9. Use of theophylline preparations or warfarin because of the theoretical possibilities, of enhanced drug effects and toxicities post influenza vaccination 10. Any medical conditions, or medication use might affect the immune response to a vaccine 11. Current alcohol, substance abuse, or systemic/psychiatric illness that potentially could interfere with patient compliance and ability to make study visit