Durability of antibody responses after receipt of the monovalent 2009 pandemic influenza A (H1N1) vaccine among HIV-infected and HIV-uninfected adults

Background: Human immunodeficiency virus (HIV)-infected persons are at risk for severe influenza infections. Although vaccination against the H1N1 pandemic influenza strain is recommended, currently there are no data on the durability of post-vaccination antibody responses in this population. Methods: HIV-infected and HIV-uninfected adults (18-50 years old) received a single dose of monovalent 2009 influenza A (H1N1) vaccine (strain A/California/7/2009H1N1). Antibody levels to the 2009 H1N1 pandemic strain were determined at day 0, day 28, and 6 months by hemagglutination-inhibition assay. A seroprotective response was a post-vaccination titer of >= 1:40 among those with a pre-vaccination level of <= 1:10. Geometric mean titers (GMT) and factors associated with higher levels were also evaluated. Results: We studied 127 participants with a median age of 35 (interquartile range (IQR) 28, 42) years. Among the HIV-infected arm (n = 63), the median CD4 count was 595 (IQR 476, 819) cells/mm(3) and 83% were receiving HAART. Thirty-five percent of all participants had a pre-vaccination level of > 1:10. HIV-infected compared to HIV-uninfected adults were less likely to generate a seroprotective response at day 28(54% vs. 75%, adjusted OR 0.23, p = 0.021) or have a durable response at 6 months post-vaccination (28% vs. 56%, adjusted OR 0.19, p = 0.005). Additionally, although pre-vaccination GMT were similar in both arms (median 7 vs. 8, p = 0.11), the GMT at 6 months was significantly lower among HIV-infected versus HIV-uninfected adults (median 20 vs. 113, p = 0.003). Among HIV-infected persons, younger age (p = 0.035) and receipt of HAART (p = 0.028) were associated with higher GMTs at 6 months. Conclusions: Despite vaccination, most HIV-infected adults do not generate durable seroprotective antibody responses to the 2009 influenza A (H1N1) virus, and hence may remain vulnerable to infection. In addition to HAART use, more immunogenic vaccines are likely needed for improving protection against influenza in this population. (C) 2011 Elsevier Ltd. All rights reserved.