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Original Contribution
August 9, 2006

Effectiveness of Haemophilus influenzae Type b Conjugate Vaccine Introduction Into Routine Childhood Immunization in Kenya

Author Affiliations

Author Affiliations: Epidemic Intelligence Service, Epidemiology Program Office, Division of Applied Public Health Training (Dr Cowgill) and Respiratory Diseases Branch (Dr Feikin), National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Ga; Wellcome Trust/Kenya Medical Research Institute (Drs Ndiritu, Mwangi, English, Newton, and Scott and Ms Nyiro) and District Public Health Office, Kilifi District Hospital (Ms Chiphatsi), Kilifi, Kenya; Haemophilus Reference Unit/WHO Collaborating Centre for Haemophilus influenzae, Respiratory and Systemic Infection Laboratory, Health Protection Agency Centre for Infections, London, England (Dr Slack); Kenya Expanded Programme on Immunization, Ministry of Health, Nairobi, Kenya (Ms Ismail and Dr Kamau); Department of Paediatrics (Dr English) and Nuffield Department of Clinical Medicine (Dr Scott), University of Oxford, John Radcliffe Hospital, Headington, Oxford, England; and Institute of Child Health, London University, London, England (Dr Newton).

JAMA. 2006;296(6):671-678. doi:10.1001/jama.296.6.671

Context Haemophilus influenzae type b (Hib) conjugate vaccine is not perceived as a public health priority in Africa because data on Hib disease burden and vaccine effectiveness are scarce. Hib immunization was introduced in Kenyan infants in 2001.

Objective To define invasive Hib disease incidence and Hib vaccine program effectiveness in Kenya.

Design, Setting, and Patients Culture-based surveillance for invasive Hib disease at Kilifi District Hospital from 2000 through 2005 was linked to demographic surveillance of 38 000 children younger than 5 years in Kilifi District, Kenya. Human immunodeficiency virus (HIV) infection and Hib vaccination status were determined for children with Hib disease admitted 2002-2005.

Interventions Introduction of conjugate Hib vaccine within the routine childhood immunization program at ages 6, 10, and 14 weeks beginning November 2001.

Main Outcome Measures Incidence of culture-proven Hib invasive disease before and after vaccine introduction and vaccine program effectiveness.

Results Prior to vaccine introduction, the median age of children with Hib was 8 months; case fatality was 23%. Among children younger than 5 years, the annual incidence of invasive Hib disease 1 year before and 1 and 3 years after vaccine introduction was 66, 47, and 7.6 per 100 000, respectively. For children younger than 2 years, incidence was 119, 82, and 16 per 100 000, respectively. In 2004-2005, vaccine effectiveness was 88% (95% confidence interval, 73%-96%) among children younger than 5 years and 87% (95% confidence interval, 66%-96%) among children younger than 2 years. Of 53 children with Hib admitted during 2002-2005, 29 (55%) were age-ineligible to have received vaccine, 12 (23%) had not been vaccinated despite being eligible, and 12 (23%) had received 2 or more doses of vaccine (2 were HIV positive).

Conclusions In Kenya, introduction of Hib vaccine into the routine childhood immunization program reduced Hib disease incidence among children younger than 5 years to 12% of its baseline level. This impact was not observed until the third year after vaccine introduction.