Epidemiology and prospects for prevention of disease due to Haemophilus influenzae in developing countries.

Haemophilus influenzae is an important cause of meningitis and severe cases of lower respiratory infection (LRI) in children in developing countries. In children with meningitis, H. influenzae type b organisms are the most frequently encountered serotype, but in some countries type a strains are also implicated. In children with LRI, type b organisms are also important, but the proportion of organisms with other serotypes and non-typable strains is greater than that associated with cases of meningitis. In developing countries, nearly all cases of H. influenzae meningitis and a substantial fraction of cases of LRI occur in children younger than one year of age. This age distribution is younger than that seen in the continental United States, where more than one-half of the cases of invasive H. influenzae disease are in children older than one year of age. New type b polysaccharide-protein conjugate vaccines are immunogenic in infants as young as two months of age and offer the promise of preventing H. influenzae type b disease in infants younger than one year of age. However, for developing countries, more complete data defining the populations at risk, the immunogenicity of candidate vaccines in children in different geographic regions, and the serotypes of the infecting organisms will be needed before successful cost-effective vaccination strategies can be devised and implemented.