Epidemiology and Infection

Research Article

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

P.  MARKEY  a1, V.  KRAUSE  a1 c1, J. W.  BOSLEGO  a2, P. M.  COPLAN  a2, J.M.  DARGAN  a2 and K. M.  KAPLAN  a2
a1 Centre for Disease Control, Territory Health Services, Darwin, Australia
a2 Merck & Co., Inc., West Point, PA, USA 19486


The Northern Territory of Australia has had historically very high incidence rates of invasive Haemophilus influenzae type b disease in children less than 5 years of age, with the burden of disease greatest among Aboriginal infants less than 12 months. This study documents the impact of conjugate Hib vaccines introduced in 1993. Immunization rates were monitored using an existing immunization register, and case finding was done retrospectively using hospital and laboratory records. Following the vaccine introduction, the incidence fell abruptly to a seventh of its pre-vaccination level, in both Aboriginal and non-Aboriginal children. The effectiveness of PRP-OMPC (PedvaxHIBTM) was 97·5% and the overall effectiveness of the vaccination programme was 86·3%. The study shows Hib immunization as an effective intervention while discussing continuing needs for Hib control in high risk populations. It also illustrates the benefit of immunization registers in the evaluation of immunization programmes and assessment of vaccine effectiveness.

(Accepted October 26 2000)

c1 Author for correspondence: Centre for Disease Control, PO Box 40596, Casuarina, NT, 0811, Australia.