An economic evaluation of vector control in the age of a dengue vaccine

Abstract

Introduction: Dengue is a rapidly emerging vector-borne Neglected Tropical Disease, with a 30-fold increase in the number of cases reported since 1960. The economic cost of the illness is measured in the billions of dollars annually. Environmental change and unplanned urbanization are conspiring to raise the health and economic cost even further beyond the reach of health systems and households. The health-sector response has depended in large part on control of the Aedes aegypti and Ae. albopictus (mosquito) vectors. The cost-effectiveness of the first-ever dengue vaccine remains to be evaluated in the field. In this paper, we examine how it might affect the cost-effectiveness of sustained vector control.

Methods: We employ a dynamic Markov model of the effects of vector control on dengue in both vectors and humans over a 15-year period, in six countries: Brazil, Columbia, Malaysia, Mexico, the Philippines, and Thailand. We evaluate the cost (direct medical costs and control programme costs) and cost-effectiveness of sustained vector control, outbreak response and/or medical case management, in the presence of a (hypothetical) highly targeted and low cost immunization strategy using a (non-hypothetical) medium-efficacy vaccine.

Results: Sustained vector control using existing technologies would cost little more than outbreak response, given the associated costs of medical case management. If sustained use of existing or upcoming technologies (of similar price) reduce vector populations by 70-90%, the cost per disability-adjusted life year averted is 2013 US$ 679-1331 (best estimates) relative to no intervention. Sustained vector control could be highly cost-effective even with less effective technologies (50-70% reduction in vector populations) and in the presence of a highly targeted and low cost immunization strategy using a medium-efficacy vaccine.

Discussion: Economic evaluation of the first-ever dengue vaccine is ongoing. However, even under very optimistic assumptions about a highly targeted and low cost immunization strategy, our results suggest that sustained vector control will continue to play an important role in mitigating the impact of environmental change and urbanization on human health. If additional benefits for the control of other Aedes borne diseases, such as Chikungunya, yellow fever and Zika fever are taken into account, the investment case is even stronger. High-burden endemic countries should proceed to map populations to be covered by sustained vector control.

Fig 1. Weekly number of dengue cases with no vector control or immunization (case management only), our base model compared to published estimates of apparent cases, best estimates and 95% UIs.

The black line and grey bands represent the best estimates and uncertainty intervals for the number of dengue cases as projected by our base model; the dotted black line represents the number of dengue cases in a single, randomly selected iteration of the model; the blue bands represent uncertainty intervals for apparent cases, as published by Bhatt et al. (2013)

Fig 2. Weekly number of dengue cases with medium or high efficacy sustained vector control technologies but no immunization, best estimates.

Fig 3. Weekly number of dengue cases with high efficacy sustained vector control and/or a highly targeted immunization strategy, best estimates.

Fig 4. Probability of being most cost-effective at any given threshold, considering high-efficacy sustained vector control and a highly targeted, low-cost immunization strategy.

The solid lines are cost-effectiveness acceptability curves (CEACs) representing the probability that an intervention is cost-effective at a given threshold; the (vertical) dashed line indicates the probability that an intervention is cost-effective at a threshold equal to GDP per capita; the dotted line represents the cost-effectiveness acceptability frontier (CEAF) which represents the probability that the most cost-effective option is cost-effective at a given threshold.

Fig 5. Probability of being most cost-effective at any given threshold, considering medium-efficacy sustained vector control and a highly targeted, low-cost immunization strategy.

The solid lines are cost-effectiveness acceptability curves (CEACs) representing the probability that an intervention is cost-effective at a given threshold; the (vertical) dashed line indicates the probability that an intervention is cost-effective at a threshold equal to GDP per capita; the dotted line represents the cost-effectiveness acceptability frontier (CEAF) which represents the probability that the most cost-effective option is cost-effective at a given threshold.