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Impact of Hib immunization in Kenya

The article

Effectiveness of Haemophilus influenzae Type b Conjugate Vaccine Introduction Into Routine Childhood Immunization in Kenya. KD Cowgill, M Ndiritu, J Nyiro, et. al. JAMA, 2006;296:671-678.

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Background: The introduction of vaccines to prevent invasive disease by Haemophilus influenzae type b (Hib) in developed countries in 1987-1991 has had a profound impact on morbidity and mortality from this infection in young infants. However, this vaccine is expensive and the disease burden is incompletely defined, making cost effective analyses difficult. Although efficacy of the vaccine in has been good in other developing countries, the vaccine has not been introduced into many countries in Africa—despite financial support provided by the World Health Organization.

The question

What is the incidence of invasive Hib disease in hospitalized children before and after introduction of Hib vaccine into the routine childhood immunization schedule in Kenya?

The study

The study was conducted in a defined region of Kenya, the Kilifi District. The area was mapped, the population of children under 5 years of age estimated, laboratory tests to detect invasive Hib were introduced—including protocols as to which children would receive diagnostic studies—at the Kilifi District Hospital. A combination vaccine that contained tetanus-toxoid-conjugated Hib vaccine was introduced in November 2001 for children 6, 10 and 14 weeks of age.

Invasive Hib disease was measured for the years 2000-2005 (2 years before and 4 years after the introduction of the vaccine).

The findings

Before vaccine was introduced the incidence of invasive Hib disease in children less than 5 years of age was 66/100,000, similar to the disease burden in other countries in Africa.

Three years after introduction of the Hib vaccine, the incidence of invasive Hib disease in this region had decreased to 12% of the baseline. The effectiveness of the vaccine was 88%, similar to other countries, both developing and developed.

The relevance/bottom line

To understand the impact of vaccine introduction requires estimates of disease burden for governments to have the will to fund new immunization programs. This study demonstrated disease burden and vaccine effectiveness in a region of Kenya.

Because the findings are similar to what has been demonstrated in other developing countries, it would seem reasonable to extrapolate these data to the rest of Kenya.

NNii’s comment

Although children with serious illnesses may not have all been admitted to the study hospital and because the diagnostic studies used are insensitive, it is possible that the study may have underestimated vaccine effectiveness. Hib conjugate vaccine greatly reduced the burden of Hib disease in Kenya.

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