Immunogenicity of a monovalent 2009 influenza A (H1N1) vaccine in an immunocompromised population: a prospective study comparing HIV-infected adults with HIV-uninfected adults.

BACKGROUND: Limited data exist on the immunogenicity of the 2009 influenza A (H1N1) vaccine among immunocompromised persons, including those with human immunodeficiency virus (HIV) infection. METHODS: We compared the immunogenicity and tolerability of a single dose of the monovalent 2009 influenza A (H1N1) vaccine (strain A/California/7/2009H1N1) between HIV-infected and HIV-uninfected adults 18-50 years of age. The primary end point was an antibody titer of ≥ 1:40 at day 28 after vaccination in those with a prevaccination level of ≤ 1:10, as measured by hemagglutination-inhibition assay. Geometric mean titers, influenza-like illnesses, and tolerability were also evaluated. RESULTS: One hundred thirty-one participants were evaluated (65 HIV-infected and 66 HIV-uninfected patients), with a median age of 35 years (interquartile range, 27-42 years). HIV-infected persons had a median CD4 cell count of 581 cells/mm(3) (interquartile range, 476-814 cells/mm(3)) , and 82% were receiving antiretroviral medications. At baseline, 35 patients (27%) had antibody titers of >1:10. HIV-infected patients (29 [56%] of 52), compared with HIV-uninfected persons (35 [80%] of 44), were significantly less likely to develop an antibody response (odds ratio, .20; P = .003). Changes in the median geometric mean titer from baseline to day 28 were also significantly lower in HIV-infected patients than in HIV-uninfected persons (75 vs 153; P = .001). Five influenza-like illnesses occurred (2 cases in HIV-infected persons), but none was attributable to the 2009 influenza H1N1 virus. The vaccine was well tolerated in both groups. CONCLUSIONS: Despite high CD4 cell counts and receipt of antiretroviral medications, HIV-infected adults generated significantly poorer antibody responses, compared with HIV-uninfected persons. Future studies evaluating a 2-dose series or more-immunogenic influenza A (H1N1) vaccines among HIV-infected adults are needed (ClinicalTrials.gov NCT00996970).