Prioritizing Interventions – Targeting IRS to Maximize Effectiveness

Malaria kills a staggering number of people every year — nearly half a million. That number is unacceptable given malaria is both preventable and treatable and somewhat surprising given donors and governments spend hundreds of millions of dollars each year attempting to control malaria.

So why is that number still so high? Well, first of all, malaria is primarily in countries with largely rural and hard to reach populations. Getting to those populations is logistically complicated and costly. Secondly, the mosquitos that transmit malaria quickly adapt to resist insecticides and to evade interventions. Thirdly, the scale of the problem is massive. While there are half a million deaths and over 200 million cases annually, the population at risk is even larger – half of the global population. Half of seven billion people are at risk for malaria.

With this context, hundreds of millions of dollars in control efforts begins to sound like a drop in the bucket. In order to make the most of the resources at hand, we must maximize the impact of each dollar spent. For example, interventions like indoor residual spraying (IRS) – where spray operators move household to household spraying the walls of homes with insecticide in order to kill the malaria transmitting mosquitoes – are very effective at killing mosquitoes and reducing malaria. However, IRS is expensive. We need to ensure we are distributing IRS resources in the most strategic and likely most impactful way.

In 2017, Akros worked with the Zambia National Malaria Elimination Centre (NMEC), the Africa Indoor Residual Spray (AIRS) Project implemented by Abt Associates, and the U.S. President’s Malaria Initiative (PMI) to conduct a comparison control trial of IRS prioritization strategies. The question was simple: If we do not have enough resources to spray every house, where should we spray to see the greatest decreases in malaria incidence? Should we spray one condensed geographic area? Should we spray the areas near the health centers with the highest burden of malaria? Or, should we spray the areas predicted to have the most mosquitoes? Each of these questions defined an arm of the study; one arm targeted IRS by concentrating it in one geographic area, one arm targeted IRS by prioritizing its delivery by health facility-measured malaria burden, and one arm targeted IRS by prioritizing its delivery by predicted mosquito density due to ecological factors. The NMEC implemented each arm in two districts of Eastern Province during the 2017 IRS operations.

In each district, Akros, AIRS, and PMI assisted the NMEC to map and prioritize areas to spray according to the selected strategy. Six months after spraying, the team ran analyses looking at patterns in malaria data across the six districts. Districts using the method of prioritizing IRS according to the areas with the highest predicted densities of mosquitoes had significantly larger drops in malaria incidence than the other districts. In fact, prioritizing by mosquito density had a 13% greater decrease than spraying in a geographically concentrated area and a 63% greater decrease than spraying areas near health centers with the highest disease burden.

Why was targeting by mosquito density most effective? There are a number of potential reasons. First, the target of IRS is the vector, the mosquito, so it makes sense to spray closest to where the mosquitoes themselves are the most abundant. Second, while health centers measure burden of disease, that burden may not be coming from the people living in areas directly around the center. People often travel to health centers based on the services available, not their distance to them. This result might be counter-intuitive to many, which just reinforces why we must continue to ask and investigate these operational research questions.

While these results offer convincing evidence for using one method of prioritization over another, all of these methods require an extremely granular approach to intervention delivery. Prioritizing accurately at a sub-district level requires interventions be planned and tracked down to the household level. Conducting public health interventions at this level is becoming more and more necessary to ensure impact and cost-effectiveness, especially as progress in some of the most challenging public health problems, like malaria, stagnates. As implementers in the malaria space, we need to continue to move the needle towards this precision public health approach.

For more details about this targeted IRS trial, please click here to read the full research brief.