Evidence Required for Adoption of New Vector Control Methods in Public Health - Biological and Environmental Control of Disease Vectors - page 198

evidence needed to justify the expenditure of
public funds on such a new intervention.
Obviously, there must be clear evidence that the
new intervention will be ef ective and good value
for money compared to existing alternatives. For
this purpose, it will not normally be enough to
show that the intervention has the desired ef ect
on the vector; rather, it will be necessary to
produce trial data showing impact on
epidemiological outcomes, preferably those that
are important in public health terms.
As the evidence about a new intervention
accumulates, it is helpful at appropriate intervals
to review and summarize the evidence available
so far in order to provide the evidential basis for
development of public health policy recom-
mendations. The methods established by the
Cochrane collaboration provide a well-established
set of principles and procedures for summarizing
the results of a group of trials. However, according
to the arguments proposed in this chapter, some
addition to these methods may be required in the
case of vector control interventions. This is
because Cochrane methods assume that a group
of trials can be treated as approximate replicates
of one another, as long as the study populations,
interventions and outcomes are all carefully
matched and standardized between studies.
Unlike medical interventions, however, vector
control produces its epidemiological benefi ts
through external ef ects on mosquitoes. There-

fore, the ef ectiveness of vector control is
infl uenced by environmental factors, including
the biology and behaviour of the local vector
species and the general ecology of the setting.
Thus we may conclude that when Cochrane
methods are used to summarize a series of vector
control trials, it is necessary to defi ne and
standardize these additional contextual and
vector biology factors, as well as the study
population, intervention and outcome measures.
The same argument applies to the process
of trying to infer, from a series of trials conducted
in a few specifi c locations, some general rules as
to the settings where a particular new
intervention is and is not likely to be cost
ef ective. In ef ect, this means that the question
'Is this new intervention ef ective?' has to be
asked again and again for each new ecological
setting and each new vector species. This does
not mean that every new intervention must
always be tested against all possible target
species in all possible settings: together, trial
results from a variety of settings can be used to
develop inferences about ef ectiveness of the
intervention elsewhere. Nevertheless, this
process of generalization must be cautious,
guided by environmental and biological con-
siderations (including a good understanding of
the epidemiological mode of action), and
reinforced by careful monitoring and evaluation
of implementation programmes.

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