Dengue vector control strategies in an urban setting: an economic modelling assessment

Abstract

Background: An estimated 2·5 billion people are at risk of dengue. Incidence of dengue is especially high in resource-constrained countries, where control relies mainly on insecticides targeted at larval or adult mosquitoes. We did epidemiological and economic assessments of different vector control strategies.

Methods: We developed a dynamic model of dengue transmission that assesses the evolution of insecticide resistance and immunity in the human population, thus allowing for long-term evolutionary and immunological effects of decreased dengue transmission. We measured the dengue health burden in terms of disability-adjusted life-years (DALYs) lost. We did a cost-effectiveness analysis of 43 insecticide-based vector control strategies, including strategies targeted at adult and larval stages, at varying efficacies (high-efficacy [90% mortality], medium-efficacy [60% mortality], and low-efficacy [30% mortality]) and yearly application frequencies (one to six applications). To assess the effect of parameter uncertainty on the results, we did a probabilistic sensitivity analysis and a threshold analysis.

Findings: All interventions caused the emergence of insecticide resistance, which, with the loss of herd immunity, will increase the magnitude of future dengue epidemics. In our model, one or more applications of high-efficacy larval control reduced dengue burden for up to 2 years, whereas three or more applications of adult vector control reduced dengue burden for up to 4 years. The incremental cost-effectiveness ratios of the strategies for two high-efficacy adult vector control applications per year was US$615 per DALY saved and for six high-efficacy adult vector control applications per year was $1267 per DALY saved. Sensitivity analysis showed that if the cost of adult control was more than 8·2 times the cost of larval control then all strategies based on adult control became dominated.

Interpretation: Six high-efficacy adult vector control applications per year has a cost-effectiveness ratio that will probably meet WHO's standard for a cost-effective or very cost-effective intervention. Year-round larval control can be counterproductive, exacerbating epidemics in later years because of evolution of insecticide resistance and loss of herd immunity. We suggest the reassessment of vector control policies that are based on larval control only.

Funding: The Fulbright Programme, CAPES (Brazilian federal agency for post-graduate education), the Miriam Burnett trust, and the Notsew Orm Sands Foundation.

Figure 1. Model of predicted incidence of dengue with no vector control

The area between the dashed lines shows the 5-year vector control assessment window.

Figure 2

Effect of larval control on dengue burden

Figure 3

Effect of adult vector control on dengue burden

Figure 4. Effect of combined vector control on dengue burden

LC=larval control. AC=adult control. Adjacent numbers refer to numbers of applications.

Figure 5. Cost-effectiveness of different control strategies

LC=larval control. AC=adult control. HE=high efficacy. IE=intermediate efficacy. LE=low efficacy. The slopes of the black lines represent the incremental cost-effectiveness ratios of the non-dominated strategies.

Figure 6. Acceptability curves for control strategies for which the probability of being cost effective is greater than zero

Acceptability curves show the probability that a given intervention meets the WHO definition of cost-effective.