21st European Congress of Clinical Microbiology and Infectious Diseases

Immunogenicity and evaluation of antibodies persistence of a single-shot of 2009 pandemic influenza vaccine in HIV-infected and HIV-uninfected subjects living in a residential drug-rehabilitation community

Abstract number: O245

Pariani E., Boschini A., Amendola A., Poletti R., Begnini M., Cecconi G., Zanetti A.

Objective: To evaluate the immunogenicity and the antibodies persistence of a single-shot of 2009 pandemic influenza vaccine in HIV-infected and HIV-uninfected subjects living in a residential drug-rehabilitation community.

Methods: 109 (49 HIV-infected and 60 HIV-uninfected) subjects living in a residential drug-rehabilitation community (San Patrignano, Rimini, Italy) received intramuscularly a single-shot of a MF59-adjuvanted 2009 pandemic influenza vaccine, containing 7.5ug hemagglutinin of A/California/7/2009(H1N1v).

Subjects (26 women and 83 men) had a mean age of 39.2±11.5 years. HIV-infected patients were mainly (98%) on highly active antiretroviral therapy (HAART) regimens. They had a mean CD4+ cell count of 386.9±225.6 cells/ul and a suppressed viremia in 91.8% of the cases.

Blood samples were taken at the time of vaccination, and 1 month and 6 months post-vaccination and were evaluated for anti-A/H1N1v antibody titers by hemagglutination-inhibition (HI) test.

Results: On baseline evaluation, 4.1–5% had HI-titers to A/H1N1v of at least 1:40 in both groups. Seroconversion, defined as at least a 4-fold increase in antibody titers from baseline, was achieved in 49/49 (100%) HIV-infected subjects and in 59/60 (98.3%) HIV-uninfected ones, with the overall proportion of patients with protective titers (1:40) being 93.9% (46/49) and 100% (60/60), respectively. The geometric mean titers (GMTs) significantly (p < 0.001) increased in both HIV-infected and HIV-uninfected subjects.

Six months after vaccination the percentage of HIV-infected subjects with protective titers was lower (p < 0.05) than that found in HIV-uninfected subjects. Similarly, 6 months post-vaccination GMTs significantly (p < 0.01) decreased in both groups, but were significantly (p < 0.05) lower in HIV-infected subjects than in HIV-uninfected ones (Table).

For HIV-1-infected individuals, no significant changes either in the CD4+ cell count or in viremia were observed at any time point.

Conclusions: A single-shot of influenza A/H1N1v 2009 MF59-adjuvanted vaccine generated antibody responses possibly associated with protection one month after immunization in successfully HAART-treated HIV-infected adults, with responses comparable to those achieved in healthy adults. This 6-month follow-up suggests that protective antibody titers can be detected after a single vaccine injection in both HIV-infected and HIV-uninfected patients but with a more appreciable decrease of antibodies titers in HIV-infected ones.