| Summary: | Worldwide vaccination introduction in the National Immunization Programs have contributed to control and prevent a considerable number of diseases. This is one of most relevant Public Health resources in the area of prevention and control of diseases and epidemics. The human-restricted bacterium Haemophilus influenzae is responsible for respiratory infections in both children and adults. While colonization begins in the upper airways, it can spread throughout the respiratory tract potentially leading to severe invasive infections. H. influenzae is divided into two major groups: non-encapsulated (NCHi) and encapsulated isolates, being the last group further characterized into six antigenically distinct serotypes (a through f), which differ in chemical and antigenic composition of the polysaccharide capsule, the major virulence factor. H. influenzae serotype b (Hib) has been a major cause of morbidity and mortality, being responsible for more than 95% of invasive disease. Prevention of Hib disease started in the early 1980s, with the license of the “first-generation Hib vaccine” that contained the pure polysaccharide of the Hib capsule. This vaccine was poorly immunogenic in children younger than 18 months. In the mid-1980s and in 1990s, Hib conjugate vaccines (PRP-OMP and PRP-CRM) were evaluated and considered immunogenic in children younger than 2 years of age. These vaccines were licensed and routinely used to prevent Hib disease that dropped dramatically soon after its introduction. In 2006, the World Health Organization (WHO) universally recommended the implementation of Hib vaccination in all infant immunization programs worldwide, which is currently in use in 192 countries, including all EU/EEA member states. Recently, other formulations of vaccines, including the aggregation of several antigens in the same injection, lead to an ultimate formula of a hexavalent vaccine (Hepatitis B, Hib, Diphtheria, Tetanus, Pertussis and Polio) that have showed good results in contributing to decrease Hib disease, with increase of coverage and maintaining effectiveness of previous vaccine combinations. With decline of Hib disease, the emergence of infections by other serotypes as well as by NCHi have been observed, highlighting the need for the development of new vaccines such as a vaccine against NCHi disease. Several studies have been conducted, but the development of an effective vaccine against NCHi is still an ongoing subject of research.
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