Invasive Haemophilus influenzae disease: changing epidemiology and host-parasite interactions in the 21st century.

Introduction of Haemophilus influenzae type b (Hib) conjugate vaccines in late 1980s-early 1990s made a dramatic effect on the incidence of invasive Hib disease among children in many industrialized countries with routine Hib immunization programs. However, cases of vaccine failure and an increased susceptibility to invasive Hib as well as non-type b H. influenzae disease have been consistently reported among individuals with various congenital and acquired immunodeficiencies. Remarkably, in the 21st century, diseases due to non-type b strains of H. influenzae are becoming relatively more frequent than before. Despite the overall successful immunization against Hib, some indigenous populations, i.e. Australian Aboriginal and North American Indian children still experience increased rates of invasive H. influenzae disease. In order to monitor the evolving nature of invasive H. influenzae disease, carefully documented surveillance data is required to capture the true magnitude of the problem. Developing new vaccines against non-type b H. influenzae is a potential solution to protect some vulnerable populations against the invasive disease.