The effectiveness of conjugate Haemophilus influenzae type B vaccine in The Gambia 14 years after introduction

Abstract

Background: The Gambia was the first country in Africa to introduce conjugate Haemophilus influenzae type b (Hib) vaccine, which, as in other developing countries but unlike industrialized countries, is delivered as a 3-dose primary series with no booster. This study assessed its effectiveness 14 years after introduction.

Methods: Using methods standardized during >20 years in the study site, clinical and microbiological surveillance for invasive Hib disease (primarily meningitis) in the Western Region of The Gambia from 2007 to 2010 was complemented with studies of Hib carriage in children aged 1 to <2 years, Hib antibody levels in children aged <5 years, and Hib vaccine coverage and timing in children aged 1 to <2 years.

Results: The incidence of Hib meningitis remained low (averaging 1.3 per 100 000 children aged <5 years annually), as did the Hib oropharyngeal carriage rate (0.9%). Hib antibody levels were protective in >99% of those surveyed, albeit with lower titers in older children; and coverage of conjugate Hib vaccination was high (91% having 3 doses at 1-2 years of age) using a schedule that was delivered at median ages of 2.6 months, 4.3 months, and 6 months for the first, second, and third doses, respectively.

Conclusions: Conjugate Hib vaccine was delivered on time in a 3-dose primary series without booster to a high proportion of eligible children and this was associated with effective disease control up to 14 years after introduction. It is important that surveillance continues in this first African country to introduce the vaccine to determine if effective control persists or if a booster dose becomes necessary as has been the case in industrialized countries.

Keywords: Africa; Gambia; Hib disease; Hib vaccination; surveillance.

Figure 1.

Map of The Gambia showing the Western Region study area (shaded) containing study hospitals in Fajara, Banjul, and Sibanor. Abbreviations: MRC, Medical Research Council; RVTH, Royal Victoria Teaching Hospital.

Figure 2.

Incidence of Haemophilus influenzae type b (Hib) meningitis in children <5 years of age, cases per 100 000 per year, in the Western Region of The Gambia from 1990 to 2010.

Figure 3.

Temporal trends in Haemophilus influenzae type b (Hib) carriage in children aged 12–23 months in rural (Sibanor) and urban (Serekunda/Fajikunda) settings.