Immunogenicity of three Haemophilus influenzae type b protein conjugate vaccines in HIV seropositive adults and analysis of predictors of vaccine response

HIV-seropositive adults may be at increased risk of infection due to Haemop hilus influenzae type b (Hib) as compared with HIV-seronegative adults. Pro tein conjugate vaccines have been demonstrated to induce protective levels of antibodies against Hib in immunocompetent infants and also in HIV-seropo sitive infants. In this study we determined the immunogenicity of three pro tein conjugate Hib vaccines (PRP-D, HbOC, HbNOMP) in 135 HIV-seropositive a dults who received one dose of Hib vaccine. Anti-polyribosylribitol phospha te (PRP) antibodies were measured at 0, 1, 3 and 12 months postimmunization by the Farr method. We demonstrate that all three vaccines are highly immu nogenic and result in protective (>1.0 mu g/ml) levels of antibody. Overall the anti-PRP antibody level was >1.0 mu g/ml in 26% of patients preimmuniz ation, 91% at both 1 and 3 months, and 79% at 12 months postvaccination. Co mparison of responses to the three vaccines over time demonstrated differen ces in the mean geometric anti-PRP antibody level at 1 month (p=0.03) and t he 12 month time points (p=0.03) with lower geometric mean levels in the Hb NOMP group, though baseline differences in groups limit the interpretation of these findings. In a univariate analysis of baseline characteristics whi ch predicted poor vaccine response, low total IgG2 levels preimmunization p redicted a poor antibody response at 1 month (p < 0.01) and at 12 months (p =0.05), while low CD4 T-cell count predicted poor response at 12 months (p < 0.01). We conclude that all three US licensed protein conjugate Hib vacci nes are immunogenic in HIV-seropositive adults, and that baseline CD4 T-cel l count and IgG2 levels predict the likelihood of antibody response to vacc ine. (C) 1999 Elsevier Science Ltd. All rights reserved.