UPDATE - December 2001
A year of reckoning for Hib
|[ Picture: Lisa Jacobs ]Keep them healthy:
where vaccines against Hib have been introduced the burden of the disease has plummeted
New tools to measure the burden of a killer microbe are delivering results fast, as Phyllida Brown discovers
DESPITE claiming the lives of some 400,000 children a year, Haemophilus influenzae Type B (Hib) was for years barely acknowledged as a health threat in many countries. As recently as last year, Immunization Focus reported that some governments were unwilling to introduce a Hib vaccine because they lacked data to show the burdens of pneumonia and meningitis caused by the microbe in their populations (1).
Today, all that has changed. Officials at WHO report a sharp upsurge during 2001 in the number of countries in Africa and the Middle East that are keen to measure the burden of Hib nationally and act to control the disease. "It's catching on like wildfire," says Chris Nelson, an epidemiologist in WHO's Department of Vaccines and Biologicals.
The reasons for the sudden growth of interest in Hib are probably twofold. First, there is the obvious attraction of new resources for Hib immunization through GAVI and the Vaccine Fund. But equally important, major practical initiatives have been launched to enable countries to assess their own Hib disease burden, raise awareness of the problem and build national surveillance systems.
Hib is one of the leading causes of pneumonia and meningitis in young children, but because diagnosis is difficult and can be confirmed only where hospital and laboratory facilities are adequate, it often goes unidentified, lumped together with the other causes of pneumonia and meningitis in the countries where the burden of childhood diseases is heaviest. In this way, it has kept a disproportionately low profile for a major killer.
No longer. Starting in 1999, WHO and its collaborators had begun to develop and introduce a tool for rapidly assessing the local burden of Hib disease which, after field testing and refinement, is now published and downloadable from the WHO web (2) . And this year, WHO also launched a network for laboratory-based surveillance of bacterial meningitis in children, starting with Sub-Saharan Africa. The initiative, which is investing US$14,000 per country for training and equipment, is funded by the Gates Children's Vaccine Program at PATH and the US Agency for International Development.
The rapid assessment tool can be used to produce estimates of disease burden within about 10 days. It uses two separate methods to estimate this burden. Because pneumonia surveillance is difficult, the first method focuses on identifying cases of meningitis. To do this, officials select an area within their country whose population is well defined and search all clinical records for cases of meningitis that occurred among young children during the preceding year. These data are then used together with information on the outcome of each patient's illness and laboratory data to calculate a local estimate of Hib-related cases and deaths. The estimates are made not only for meningitis, but also for the much more widespread Hib pneumonia: using existing data, researchers estimate that there are about five cases of Hib pneumonia for every case of Hib meningitis. After conducting this exercise in several districts, national estimates are extrapolated.
Asia and the Pacific next
The tool's second method is used where clinical and laboratory records are not sufficiently complete; it is also used to complement the first method where possible. Using data for deaths in under-fives, officials identify what percentage of those deaths are due to acute respiratory infections (ARI), and then use the existing data to estimate what proportion of the ARI deaths are Hib-related. In turn, this allows an estimate of the number of Hib meningitis cases.
Countries have already moved fast to implement the tool: in Sub-Saharan Africa, Ghana, Tanzania and Uganda have conducted assessments, while in WHO's Eastern Mediterranean region, Egypt, Iran, Jordan, Oman and Yemen have also completed their assessments. Next year, Zimbabwe, Lebanon, Libya and Pakistan are among those countries planning to go ahead, and activities are also expected to spread to south Asia and the Pacific with assessments planned in Bangladesh, Malaysia, the Maldives and Thailand.
Meanwhile, the network for surveillance of paediatric bacterial meningitis has already conducted training sessions for paediatricians, microbiologists and data managers drawn from the largest hospital in the capital city of each of 27 countries in Sub-Saharan Africa, together with immunization officials from each health ministry.
"Bringing together all members of the surveillance team at one time has contributed to the early success of the programme and has helped to raise awareness," says Nelson. The training covers surveillance activities in the clinic and lab, and, under a regional coordinator, the initiative is providing each country with a manual (3) , laboratory reagents, and laptop computers for data management and reporting.
In Addis Ababa, Ethiopia, earlier this month, Dr Themba Mhlanga, coordinator of the network in Sub-Saharan Africa, gave an upbeat assessment of progress. "Just six months after the first training session we can already see the success of this programme, with half of all countries reporting surveillance data on a monthly basis," he told the Ninth Meeting of the African Task Force on Immunization in Africa. Next year, the surveillance network is expected to expand to the Eastern Mediterranean region.
So far, only Ghana, Kenya, Malawi, Rwanda and Uganda have been allocated Hib vaccines (in combination form) by GAVI and the Vaccine Fund. Additional countries are not likely to receive Hib vaccine until next year at the earliest, because of a shortfall in the supply of the existing combinations (see article in this issue, page 2 ). But, judging from the experiences of countries in Latin America, Europe and North America, the impact of the vaccine is likely to be dramatic once it is introduced: Hib could be facing virtual elimination within years in the countries where immunization is fully implemented. For now, however, the onus is on countries to establish paediatric bacterial meningitis surveillance and measure their Hib burden. So far, from the commitment shown by the first round of countries, there is every sign of rapid progress towards this end.
References and resources
(1) The invisible culprit. Immunization Focus, August 2000
(2) Estimating the local burden of Hib disease preventable by vaccination (WHO/V&B/01.27)
An Excel file
See also associated documents:
Expert review of a tool for rapidly assessing Haemophilus influenzae type b (Hib) disease burden (WHO/V&B/01.25) PDF
and Estimating the potential cost-effectiveness of using Haemophilus influenzae type b (Hib) vaccine. Field test version 1 (WHO V&B/01.36).
(3) The WHO/AFRO Hib-Paediatric Bacterial Meningitis (Hib-PBM) Surveillance Network: Surveillance Manual. Field Test Version, July 2001.
Management guidelines for the introduction of Hib vaccine are also available from WHO, including information for health workers and parents (WHO/V&B/00.05).
A fact sheet on Hib is also available (WHO/V&B/01.29).
Immunization Focus December 2001 - Contents