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2001 contents page
A year of reckoning for Hib
New tools to measure the burden of
a killer microbe are delivering results fast, as Phyllida Brown
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.
Keep them healthy:
where vaccines against Hib have been introduced the burden
of the disease has plummeted
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. http://www.VaccineAlliance.org/newsletter/aug2000/feature.html
the local burden of Hib disease preventable by vaccination (WHO/V&B/01.27)
An Excel file at http://www.who.int/vaccines-documents/excel/www625.xls
See also associated documents:
Expert review of a tool for
rapidly assessing Haemophilus influenzae
type b (Hib) disease burden (WHO/V&B/01.25) http://www.who.int/vaccines-documents/DocsPDF01/www604.pdf
and Estimating the potential cost-effectiveness of using
Haemophilus influenzae type b (Hib) vaccine. Field test version
1 (WHO V&B/01.36). http://www.who.int/vaccines-documents/DoxGen/H3DoxNew.htm
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) at http://www.who.int/vaccines-documents/DoxGen/H3DoxNew.htm.
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