Haemophilus influenzae type B infection.

Haemophilus influenzae type B infection* 1. Brief description of the condition/disease Haernophilus influzenZae type b (Hib) is a bacterium that causes meningitis, pneumonia. septicaemia, and other severe, invasive infections Meningitis is char- acterized by intection of thic spinal fluid and the meninges, a membrane that surrounds the brain In the USA and other developed countries, approxi- mately 5% of patients with meningitis die. and up to 30% ot survivors lhave long-term disabilities ranging from hearing loss to sevee mental retardation. In developing countries. up to 50% of Hib patients die in sonle settings. 2. Current global burden and rating within the overall burden of disease In the absence of vaccination. Hib was consistentlv identified as the leading cause of bactcrial meninigitis among under-5-year-olds in developed countries Betore vaccination in the USA. an estinmated I of every 200 children had an invasive Hib infection be- fore thc age 5 years. In dcveloping countries, Hib is the leading cause of bacterial meningitis-associated deaths and the sccond leading cause of bacterial pneumonia deaths. Globally. Hib meningitis and pneum-nonia cause 380000-500(N0 deaths among under-5-year-olds each year. Accurate Hib disease incidence data are lacking for manv parts of Asia and the Pacific Rim. 3. Feasibility (biological) of elimination/eradication The biological feasibilitv ot Hib eradication is diffi- cult to delei mine. but several aspects of Hib discase andtHib vaccines make elimination possible. Hib is a unliquelv human patlhooen with no known reservoir ill the environment. Hib polysaccharide-protein conjugatc vaccines arc hlighlv effectivc (efficacy of Contibuted by Onn Levine Jay Wer'ger Yand Bradley Perkins Nancy Rosenstein and Anne Schucnat Centers for Disease Con- trol and Prevention. Atlanta. GA, USA. and the Global Programme for Vaccines. WHO, Geneva. Swnizerland. 90-100%) in preventing disease, and should provide long-lasting protcction. Hib conjugate vaccines also can interrupt transmission by preventing asympto- matic carriage and are thereby able to protect unvaccinated persons through herd immunity. At the practical level, Hib conjugate vaccines arc still too expensive for many countries to use, they require more than one dose to provide substantial protec- tion, and not all countries may be able to achleve Lhe levels of vaccination coverage needed for elimina- tion. Thus, programmatic obstacles are the major bairiers to eliminationi. The feasibility of eradicating Hib is morc diffi- cult to determine. At the molecular level. elminat- ing the genetic material that codes for the type b capsule is more difficult than climinating the appar- cnt occurrence of type b infections. With more research into the molecular biology of Hib and tur- ther expeenence witlh the vaccines. It may bc possible to determine more accurateIy the leasLbility of eradication 4. Estimated costs and benefits of elimination/eradication Although economic analyses 01' 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 currcnt vaccination coverage rates, suchl a programme could prevent 58-83% of all Hlib-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 otlher new immnunizations and with othier life-saving interven- tioiis. The analysis. however, assuned that vaccine could be purchased at US$ I per dose. a price that slhould be attainablc but is still lower tlian tile cui- rent price 5. Key strategies to accomplish the objective(s) Routine vaccination through national programmes is tlhe cornerstone of control of Hib disease. Efforts to mnaintain hiah coverage and timely vaccination will improve the effectiveness of this control strategy. Ensuring a steadv', affordable supply of Hib vaccine for dcveloping countries will be essential. Efforts Bulletn of the World Health Organhzation, 1998, 76 (Suppl 2). 131-132 131 Haemophllus influenzae type B infection to elimmate ilb in countries with moderate-to- poor vaccination coverage will depend on the ability of the [Jib vaccination programme to inter- rupt transmission and thereby provide herd immu- nitv. Whether routine Hib vaccination will result in herd immunity in developing countries is still unclear. Further expenence with Hib vaccines in developing countries may provide insights to novel strategies for maximizing the herd immunity effects of vaccination. Surveillance for [fib disease, including laboratory identification of the bactenum, wvil be required to monitor the impact of vaccination. 6. Research needs Because experience with -ib conjugate vaccines is relatively limited (about 10 years), continued assess- ment is needed of the long-term impact on immuniLty and on carriage rates. The mechanism for interrupt- ing Hib transmission is still unknowmn Continued ef- forts on new and improvcd Hib vaccines, which miay be less expensive or provide imunity with fewer doses, are warranted. Additionally, research is needed to determine if it is possibie to eradicate the gene for the type b capsule trom populations of H. influenzae bactena. Because an accurate surveillance programme Nwith relatively simple diagnostic methods would be critical during an eradication campaign, a non- invasive test for confirmation of Hib meningitis should be developed Such a scnLinel test should be supplemented with a standardized protocol lo quan- tify the associated impact on Hib carnage. In many countries, particularly in Asia. the bur- den of [Jib disease remains largely undefined. Be- cause the political will to pursue vaccination will depend in large part on the magnitude of the Hib disease burden locally, additional efforts are needed to quantify the burden or Hib disease wlvere it re- mains undefincd 7. Status of eliminationferadication efforts to date The widcspread use of [Hib conjugate vaccines for routine vaccination of infants and young children has dramatically reduced the incidence of the disease and the transmission of fHib organisms in several developed countries. In the Nordic countries (Fin- land. [ccland, Sweden, Norway, and Denmark) rou- tine vaccination has essentially eliminated Hib disease, and in Finland and Iceland carnage in young childrcn is no longer detected. In the USA, the im- pact ot [Jib vaccinatLon has been equally dramatic: thc incidence of Hib disease in young children has declined by >95%, and good evidence exists that Hib vaccination has interrupted transmission and protected unvaccinated children by herd immunity. In developing countries. however, where the epide- miology of [Jib disease differs substantially trom the epidemiology in the USA and Europe. the impact of widespread vaccination is still unclear. 8. Principal challenges to elimination/eradication The current price of Hib conjugatc vaccines is the principal obstacle to the wider control of Hib disease globally. Efforts to ensurc access to a steady, inex- pensive supply of vaccine will be needed. Hib vaccines combined with other newcr vaccines having a broader impact on meningitis and acute respiratory infections may be more acceptable. A lack of inlor- maLion on the burden of disease in some regions also limits the vaccine's uptake in somne regions that can afford it. Elimination of Hib invasive disease nmay be possible in the future, but additional expericnce with the use ot Hib conjugate vaccmes for control ot Hib disease in noniiidustrialized countries will be nceded bcfore Lhe feasibility of eradication can be evaluated adequately. WHO Bulletin OMS Vol 76, Suppl 2 1998132