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Research into Haemophilus influenzae, a commensal and pathogen of humans, has resulted in major scientific contributions to biology. The first endonucleases (restriction enzymes), which paved the way for the new genetics, and the DNA used to obtain the first complete genome sequence of a free-living organism were obtained from H. influenzae. Prevention of invasive bacterial infections of infants, such as meningitis, has been achieved using a novel class of vaccines, of which the glycoconjugates of H. influenzae were the first to be licensed. Originally fallaciously proposed to be the aetiological agent of epidemic influenza, now known to be caused by a virus, H. influenzae is a pathogen of global public health importance. Research into the pathogenesis of the infections it causes (for example, meningitis, septicaemia, pneumonia and otitis media) are case studies in understanding the molecular basis of the variation in gene expression and gene sequences that are critical to its commensal and virulence behaviour and for the strategies that can be pursued to prevent H. influenzae diseases through vaccines.

Haemophilus influenzae type b (Hib) vaccination coverage and disease incidence were measured among preschool-aged children residing in inner-city Los Angeles. Among children 1.5 to 14 months of age, vaccination coverage of at least one dose increased from 0% in 1990 to 82% (95% confidence interval [CI] = 73%, 91%) in 1992. Among children 15 to 59 months old, vaccination coverage of at least one Hib dose administered at or after age 15 months increased from 35% (95% CI = 29%, 41%) in 1990 to 63% (95% CI = 56%, 70%) in 1992. Although Hib vaccination has reduced disease incidence in this population, greater use of vaccine can result in further reductions. (Am J Public Health. 1994;84:1154-1157), The number of infants younger than 15 months vaccinated against Hemophilus influenzae type B (Hib) appears to have increased significantly between 1990 and 1992 in Los Angeles. Hib infection can lead to bacterial meningitis which may cause death or permanent injury. Hib vaccines for children younger than 18 months only became available in 1987. Households within a 53-census-tract area were sampled in 1990, 1991 and 1992. Adult members of the households provided written records of infants' vaccinations. The proportion of infants between 1.5 and 14 months of age vaccinated with at least one dose of Hib vaccine increased from 0% in 1990 to 82% in 1992. At the time of the 1992 survey, significantly larger numbers of children had been vaccinated with second and third doses of the vaccine before they were 15 months old. Additionally, the incidence of Hib disease in children younger than five years decreased by 69% between 1986 and 1992.