Elimination of Haemophilus influenzae type b (Hib) disease from The Gambia after the introduction of routine immunisation with a Hib conjugate vaccine: a prospective study

Routine immunisation of infants in The Gambia with a Haemophilus influenzae type b (Hib) polysaccharide-tetanus toxoid conjugate vaccine began in May, 1997. We investigated the effectiveness of the vaccine when delivered through the expanded programme on immunisation and the effect of national immunisation on incidence of Hib disease. Surveillance for Hib disease was maintained in the western half of The Gambia using standard methods with an emphasis on meningitis. We estimated vaccine efficacy using the case control method, and vaccine coverage and population denominators for incidence rates using a cluster sample survey. Prevalence of Hib carriage in a sample of 1–2-year old children attending health centres for vaccination was ascertained with oropharyngeal swabs plated onto antiserum agar. Between May, 1997, and April, 2002, a total of 5984 children were examined for possible Hib infections. 49 children had Hib disease, 36 of whom had meningitis. The annual incidence rates of Hib meningitis before any use of the vaccine (1990–93) dropped from over 200 per 100 000 children aged younger than 1 year to none per 100 000 in 2002, and from 60 to no cases per 100 000 in children younger than 5 years. The prevalence of Hib carriage decreased from 12% to 0·25% (p