Dr. Shabir A. Madhi and associates of the University of the Witwatersrand in Johannesburg evaluated outcomes in infants vaccinated against Hib in 1998 as part of a phase III trial. Almost 20,000 children, for whom the prevalence of HIV was estimated to be 6.03%, were vaccinated. The incidence of invasive Hib disease until September 2000, was compared to that of approximately 22,000 children born in 1997 who did not receive Hib vaccination.

The estimated relative annual incidence rates in the unvaccinated, HIV-seronegative children, was 170 per 100,000 children, Dr. Madhi's team reports in the April issue of The Pediatric Infectious Disease Journal. The incidence rate was nearly six times higher among the unvaccinated children who were HIV-positive.

In the children who received Hib conjugate vaccine, nine children contracted invasive Hib disease, seven of whom were infected with HIV. These results translate to a vaccine efficacy of 96.5% in the HIV-uninfected children and of 43.9% in those with HIV disease. The overall Hib vaccine effectiveness was 83%.

Dr. Madhi's team reports that three vaccinated HIV-infected children who contracted Hib infections were evaluated for Hib IgG antibodies. Their titers proved to be high enough that, under normal circumstances, they would have exhibited short-term immunity. The researchers propose that these children's antibodies were functionally impaired.

Therefore, the South African investigators recommend that clinicians "perform functional antibody assays in HIV-1 infected children who are recognized to have impaired cell-mediated and B lymphocyte activity."

Pediatr Infect Dis J 2002;21:315-321.