Haemophilus Influenzae Type B Infection(*)

Article excerpt

1. Brief description of the condition/disease

Haemophilus influenzae type b (Hib) is a bacterium theft causes meningitis, pneumonia, septicaemia, and other severe, invasive infections. Meningitis is characterized by infection of the spinal fluid and the meninges, a membrane that surrounds the brain. In the USA and other developed countries, approximately 5% of patients with meningitis die, and up to 30% of survivors have long-term disabilities ranging from hearing loss to severe mental retardation. In developing countries, up to 50% of Hib patients die in some settings.

2. Current global burden and rating within the overall burden of disease

In the absence of vaccination, Hib was consistently identified as the leading cause of bacterial meningitis among under-5-year-olds in developed countries. Before vaccination in the USA, an estimated 1 of every 200 children had an invasive Hib infection before the age 5 years. In developing countries, Hib is the leading cause of bacterial meningitis-associated deaths and the second leading cause of bacterial pneumonia deaths. Globally, Hib meningitis and pneumonia cause 380 000-500 000 deaths among under-5-year-olds each year. Accurate Hib disease incidence data are lacking for many parts of Asia and the Pacific Rim.

3. Feasibility (biological) of elimination/eradication

The biological feasibility of Hib eradication is difficult to determine, but several aspects of Hib disease and Hib vaccines make elimination possible. Hib is a uniquely human pathogen with no known reservoir in the environment. Hib polysaccharide-protein conjugate vaccines are highly effective (efficacy of 90-100%) in preventing disease, and should provide long-lasting protection. Hib conjugate vaccines also can interrupt transmission by preventing asymptomatic carriage and are thereby able to protect unvaccinated persons through herd immunity. At the practical level, Hib conjugate vaccines are still too expensive for many countries to use, they require more than one dose to provide substantial protection, and not all countries may be able to achieve the levels of vaccination coverage needed for elimination. Thus, programmatic obstacles are the major barriers to elimination.

The feasibility of eradicating Hib is more difficult to determine. At the molecular level, eliminating the genetic material that codes for the type b capsule is more difficult than eliminating the apparent occurrence of type b infections. With more research into the molecular biology of Hib and further experience with the vaccines, it may be possible to determine more accurately the feasibility of eradication.

4. Estimated costs and benefits of elimination/eradication

Although economic analyses of programmes to eliminate/eradicate Hib have not been carried out, a recent analysis of the cost-effectiveness of routine Hib vaccination globally determined that, at current vaccination coverage rates, such a programme could prevent 58-83% of all Hib-related deaths and Hib-related disability-adjusted life years (DALY) lost at a cost of US$ 35-53 per DALY saved. This cost-per-DALY saved compares favourably with other new immunizations and with other life-saving interventions. The analysis, however, assumed that vaccine could be purchased at US$ 1 per dose, a price that should be attainable but is still lower than the current price.

5. Key strategies to accomplish the objective(s)

Routine vaccination through national programmes is the cornerstone of control of Hib disease. Efforts to maintain high coverage and timely vaccination will improve the effectiveness of this control strategy. Ensuring a steady, affordable supply of Hib vaccine for developing countries will be essential. Efforts to eliminate Hib in countries with moderate-to-poor vaccination coverage will depend on the ability of the Hib vaccination programme to interrupt transmission and thereby provide herd immunity. …