The effectiveness of Haemophilus influenzae type b conjugate vaccines in ahigh risk population measured using immunization register data

The Northern Territory of Australia has had historically very high incidenc e rates of invasive Haemophilus influenzae type b disease in children less than 5 years of age, with the burden of disease greatest among Aboriginal i nfants less than 12 months. This study documents the impact of conjugate Hi b vaccines introduced in 1993, Immunization rates were monitored using an e xisting immunization register, and case finding was done retrospectively us ing hospital and laboratory records. Following the vaccine introduction, th e incidence fell abruptly to a seventh of its pre-vaccination level, in bot h Aboriginal and non-Aboriginal children. The effectiveness of PRP-OMPC (Pe dvaxHIB (TM)) was 97.5 % and the overall effectiveness of the vaccination p rogramme was 86.3 %. The study shows Hib immunization as an effective inter vention while discussing continuing needs for Hib control in high risk popu lations. It also illustrates the benefit of immunization registers in the e valuation of immunization programmes and assessment of vaccine effectivenes s.