The investigators study is being conducted to evaluate and compare the seroresponses of the novel H1N1 vaccination among HIV positive and negative persons receiving the novel H1N1 vaccination as part of routine clinical care, with secondary objectives examining the impact of prior seasonal vaccinations on subsequent seroresponse to the novel H1N1 vaccination, determining potential reactions (local or systemic) to this new vaccine among patients, and assessing for potential immunologic/virologic changes (in CD4/HIV RNA levels) after H1N1 vaccination among HIV patients. Finally, the investigators will collect data on influenza-like illnesses (ILI) and H1N1 events during the study follow-up period and influenza isolates causing ILI events will be genetically characterized.
