Immunogenicity and effectiveness of Haemophilus influenzae type b conjugate vaccine in HIV infected and uninfected African children

The quantitative (anti-Hib capsular polysaccharide antibody concentrations; anti-HibPS) and qualitative (bactericidal activity and avidity) aspects in immune responses to Haemophilus influenzae type b polyribosyl ribitol phospshate-CRM197 conjugate vaccine (HibCV; HibTiter®) were evaluated in 66 HIV infected children not receiving anti-retroviral therapy and 127 HIV uninfected children. Surveillance was conducted for invasive Hib disease in a cohort of 39 865 (approximately 6.4% of whom were HIV infected) children from March 1998 to June 2004. HIV infected children had lower anti-HibPS geometric mean antibody concentrations 1 month post-immunisation than HIV uninfected children (P < 0.00001) and were less likely to have anti-HibPS antibody concentrations of ≥1.0 μg/ml (RR 0.54; 95% CI 0.43–0.69). A lower proportion of HIV infected children than HIV uninfected children (RR 0.78; 95% CI 0.66–0.93) had measurable anti-Hib serum bactericidal activity (SBA) and the HibPS antibody concentration required for 50% killing of Hib bacteria was greater among HIV infected than HIV uninfected children (P = 0.001). The estimated risk of HibCV failure was 35.1-fold greater (95% CI 14.6–84.6) amongst HIV infected than HIV uninfected children.