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The effectiveness of Haemophilus influenzae type b conjugate vaccines in a high risk population measured using
P Markey1, V Krause, J W Boslego
1Centre for Disease Control, Territory Health Services, Darwin, Australia.
Insights
Haemophilus influenzae type b (Hib) conjugate vaccines dramatically reduced invasive Hib disease in Northern Territory children. The vaccination program achieved 86.3% effectiveness, highlighting immunization
Area of Science:
- Pediatrics
- Immunology
- Public Health
Background:
- Historically high rates of invasive Haemophilus influenzae type b (Hib) disease in children under 5 in Australia's Northern Territory.
- Disproportionately high disease burden among Aboriginal infants under 12 months.
Purpose of the Study:
- To document the impact of conjugate Hib vaccines introduced in 1993 on disease incidence.
- To evaluate the effectiveness of the Hib vaccination program and specific vaccines.
Main Methods:
- Retrospective case finding using hospital and laboratory records.
- Monitoring immunization rates via an existing immunization register.
- Calculating vaccine effectiveness for PRP-OMPC (PedvaxHIB) and the overall program.
Main Results:
- Abrupt sevenfold decrease in invasive Hib disease incidence post-vaccine introduction.
- High vaccine effectiveness: 97.5% for PRP-OMPC and 86.3% overall.
- Significant reduction observed in both Aboriginal and non-Aboriginal children.
Conclusions:
- Hib immunization is a highly effective intervention for controlling invasive Hib disease.
- Ongoing strategies are needed for Hib control in high-risk populations.
- Immunization registers are valuable for program evaluation and vaccine effectiveness assessment.
Abstract:
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 (PedvaxHIB) 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.