Safety of and Immunogenicity to an H1N1 Influenza Vaccine in HIV-infected Adults

Inclusion Criteria - for all participants * Both genders, aged between 18 and 59 years; * Capacity to give informed consent voluntarily to participate in the study; * Study participants with reproductive potential (defined as girls after menarche or women who have not reached menopause at least during 24 consecutive months, or who menstruated during the past 24 months, or have not undergone surgical sterilization) must have pregnancy test negative results, in blood or urine, at screening and in the vaccine application days. If they have sexual practices likely to promote pregnancy, the participants must use some form of contraception during the study period. At least one of the following methods MUST be properly used: Condoms (male or female, Hormonal contraceptive. * Laboratory results in the study screening: hemoglobin \> 8.0 g/dL; Direct bilirubin \< 2.5 x the upper limit of normal; Alanine aminotransferase, ALT (SGPT) and aspartate aminotransferase, AST (SGOT) \< 3 x the upper limit of normal; Platelet count \> 100.000/mm3 Inclusion Criteria - unique to the participants with HIV infection: * HIV-1 infection (as evidenced by rapid HIV testing or ELISA kit approved and confirmed by repeating the ELISA, IFA, Western blot, HIV-1 plasma viral load) at any time before entering the study. * Without changing the antiretroviral treatment within 8 weeks prior to the screening for the study: If the volunteer is receiving HAART he/she is required to be using the same regimen within at least 8 weeks before screening. Changes in antiretroviral dosage within 8 weeks prior to entering the study are permitted. In addition, the exchange of pharmacological formulation (eg. the conventional formulation for combination formulations) is allowed. If the volunteer is not on regular antiretroviral treatment, he/she should not have received any dose of any antiretroviral within 8 weeks prior to screening, including for the prevention of HIV vertical transmission (previous prophylactic and therapeutic regimens are allowed) * Without planning to change or start HAART in the next 6 months. Inclusion criteria - unique to the participants without HIV infection (control group): * HIV-negative test result documented by rapid test approved in Brazil * Health professionals with indication of receiving H1N1 virus vaccine Exclusion Criteria: * Use of any systemic anticancer or immunomodulator treatment, corticosteroid, experimental vaccines, interleukins, interferons, growth factors or intravenous immunoglobulin (IVIG) within 45 days prior to entry into the study. * Pregnancy or lactation. * Allergy and/or sensitivity or any known hypersensitivity to residues present in the vaccine (egg, chicken protein, egg albumin, formaldehyde, gentamicin sulphate and sodium deoxycholate) and/or thimerosal. * Use of alcohol or addiction or other conditions which in the opinion of the site's investigator, may interfere with compliance to the study requirements. D5. Serious illness requiring systemic treatment and/or hospitalization within 45 days prior to entry into the study * Severe febrile illness or acute infection at the time of screening for the study and/or days of vaccination * Vaccination against seasonal influenza in the last 12 months prior to study entry * Previous vaccination against influenza A H1N1 * History or family history of Guillain-Barré Syndrome (parents, siblings, half-siblings or children). * Diagnosis of neurological condition including (but not limited to) the absence of deep tendon reflexes, Achilles and patellar, in both legs (four missing) in the last six months. * Disproportionate force loss in lower limb(s) compared to the upper limbs in the last six months.