Malaria epidemiology and economics: the effect of delayed immune acquisition on the cost-effectiveness of insecticide-treated bednets

An understanding of the epidemiology of a disease is central in evaluating the health impact and cost-effectiveness of control interventions. The epid emiology of life-threatening malaria is receiving renewed interest, with co ncerns that the implementation of preventive measures such as insecticide-t reated bednets (ITNs) while protecting young children might in fact increas e the risks of mortality and morbidity in older ages by delaying the acquis ition of functional immunity This paper aims to illustrate how a combined a pproach of epidemiology and economics can be used to (i) explore the long-t erm impact of changes in epidemiological profiles, and (ii) identify those variables that are critical in determining whether an intervention will be an efficient use of resources. The key parameters for determining effective ness are the protective efficacy of ITNs (reduction in all-cause mortality) , the malaria attributable mortality and the increased malaria-specific mor tality risk due to delays in the acquisition of functional immunity. In par ticular, the analysis demonstrates that delayed immune acquisition is not a problem per se, but that the critical issue is whether it occurs immediate ly following the implementation of an ITN programme or whether it builds up slowly over time. In the 'worst case' scenario where ITNs immediately incr ease malaria-specific mortality due to reduced immunity, the intervention m ight actually cost lives. In other words, it might be better to not use ITN s. On the other hand, if reduced immunity takes two years to develop, ITNs would still fall into the category of excellent value for money compared to other health interventions, saving a year of life (YLL) at a cost of betwe en US$25-30. These types of calculations are important in identifying the p arameters which field researchers should be seeking to measure to address t he important question of the net impact of delaying the acquisition of immu nity through preventive control measures.