The efficacy in Navajo infants of a conjugate vaccine consisting of Haemophilus influenzae type b polysaccharide and Neisseria meningitidis outer-membrane protein complex

Infection by Haemophilus influenzae type b bacteria can lead to a variety of serious complications, including meningitis, in which the membranes that surround the brain and spinal cord become inflamed. Some population groups, including certain Native American tribes, have infection rates several times higher than the general population. To evaluate the effectiveness of a new vaccine among Navajo infants, a controlled study was carried out. Infants aged between 42 and 90 days were randomly assigned to receive either the vaccine (2,588 subjects), a conjugate of H. influenzae type b capsular polysaccharide and parts of the outer-membrane protein complex (OMPC) of Neisseria meningitidis serogroup B, or a placebo (2,602 subjects), an inactive substance. Second injections were given between the ages of 70 and 146 days. Blood samples were obtained at different points during the study and analyzed to determine the infants' levels (titers) of antibodies against H. influenzae; the safety and efficacy of the vaccine were also monitored. The study began in July 1988; by August 1990, after 23 cases of H. influenzae infection had occurred, it was decided to stop the study. The group that had received the vaccine had far fewer cases than the placebo group (1 case versus 22 cases) by the age of 18 months. Thirteen of the 22 placebo cases developed meningitis. No infections occurred in the vaccine group between the first and second doses of vaccine; eight occurred in the placebo group. Antibody levels did not increase noticeably after the second vaccination, but the vaccine was effective up until 18 months of age. The overall efficacy of the H. influenzae type b OMPC vaccine was more than 90 percent in this population. This was much higher than the efficacy reported for another conjugate vaccine in another study of Native Americans in Alaska. Use of this vaccine should eliminate H. influenzae type b infection. (Consumer Summary produced by Reliance Medical Information, Inc.)