Haemophilus influenzae Type B

Abstract

Prior to widespread use of vaccine, Haemophilus influenzae type b (Hib) was the leading cause of bacteremia, pneumonia, and meningitis among US infants and young children. Invasive Hib disease was estimated to infect 1 in 200 children younger than 5 years of age in the USA. Hib vaccines were introduced into the national pediatric immunization schedule in the late 1980s. Almost immediately following their widespread use, there was a dramatic decline in disease incidence. While developed countries were early adopters of the conjugate Hib vaccine, developing countries were slower to do so for a variety of reasons, including but not limited to the perceived lack of disease burden to justify adding another vaccine to the schedule and the associated financial constraints of being able to do so. The African nation of Gambia, however, introduced Hib vaccine in 1997, being among the first African countries to routinely immunize their children against this infection. Prior to vaccine initiation, the incidence of Hib meningitis in The Gambia was 297 per 100,000 children younger than 1 year of age and 60 per 100,000 children younger than 5 years of age. Only 55% of infected children fully recovered (Bijlmer et al., J Infect Dis 161:1210–5, 1990). Although the incidence of Hib meningitis in The Gambia was similar to that in the USA, Gambian children were significantly more likely to have devastating outcomes (Bijlmer et al., J Infect Dis 161:1210–5, 1990). Five years after introduction of conjugate Hib vaccine in The Gambia, the incidence of Hib meningitis decreased to zero in children less than 5 years of age (Oluwalana et al., J Pediatr 163:S4–7, 2013; Adegbola et al., Lancet 366:144–50, 2005). In addition, Hib nasopharyngeal carriage among toddlers decreased from 12% to 0.25% during this time period (Adegbola et al., Lancet 366:144–50, 2005). The data from The Gambia highlight the effectiveness of conjugate Hib vaccines in the prevention of invasive disease. Observations regarding the effectiveness of Hib vaccine are not isolated to the USA and The Gambia. Similar impressive results have been achieved in every part of the world where Hib vaccination has been introduced.