Physical Durability and Insecticidal Efficacy of Interceptor® G2, PermaNet® 3.0, Yahe® and Olyset® Brand Insecticide-Treated Nets between 2020 and 2023, Rwanda

Malaria remains one of the most persistent threats to human health across sub-Saharan Africa, a disease transmitted when a mosquito bites a person. For decades, the primary defense against this threat has been the insecticide-treated net, a simple mesh barrier that serves a dual purpose. First, it acts as a physical shield, stopping mosquitoes from reaching the skin. Second, it is coated with chemicals that kill or repel the insects that land on it. While these nets have saved millions of lives, they are not indestructible. Over time, the fabric tears, the holes grow, and the chemicals wash away or fade. When a net develops too many holes or loses its insect-killing power, it stops protecting the people sleeping beneath it. Understanding exactly how long these nets last in real-world conditions, and what causes them to fail, is critical for health officials who must decide when to replace them and which types to buy for future campaigns.

In Rwanda, researchers set out to track the life and death of four different brands of these nets over a three-year period. Following a massive distribution campaign in 2020 that handed out millions of nets, teams monitored a specific group of households in four different districts. They did not just ask people if their nets were still there; they physically inspected the nets for holes, measured the size of any tears, and collected samples to test in laboratories. The goal was to see how long the nets remained in good enough condition to be useful, and whether they still possessed enough insecticide to kill mosquitoes that had developed resistance to older chemicals. The study compared four distinct types of nets: two that relied on a single type of insecticide, one that combined a standard insecticide with a synergist to boost its effect, and one that used two different active ingredients to attack mosquitoes in multiple ways.

The results revealed that not all nets are created equal, and their lifespan depends heavily on where they are used and how they are treated. After three years, the nets varied significantly in how long they survived. The nets distributed in the Ruhango district, which were a single-ingredient type, lasted the longest, with a median useful life of 4.3 years. In Kicukiro, a peri-urban area, the nets with the synergist lasted about 4.0 years. The nets in Karongi, which used two active ingredients, survived for roughly 3.1 years. However, the nets in the Burera district, a single-ingredient type, fell apart the fastest, with a median survival of only 2.3 years. This means that in Burera, half of the nets were no longer serviceable before they even reached the standard three-year mark often assumed for these tools. The study found that the physical condition of the nets was the main driver of this difference; the nets in Burera had the highest number of holes and the most tears, while the nets in Ruhango remained the most intact.

Physical damage was not the only concern; the chemical power of the nets also faded over time. By the end of the study, the ability of the nets to kill mosquitoes had dropped considerably across the board. For the single-ingredient nets, the chemical content had decreased so much that they were barely effective against mosquitoes that were not resistant to the insecticide. Even the more advanced nets, which were designed to handle resistant mosquitoes, showed a decline. The nets with the synergist lost a large portion of their boosting chemical, and the two-ingredient nets saw a significant drop in both of their active components. While the advanced nets still performed better than the basic ones against resistant mosquitoes, their protective power was clearly weakening as the years passed. This suggests that relying on a single batch of nets for a long period might leave communities vulnerable as the chemicals degrade.

The researchers also looked closely at the human behaviors that influenced how long a net lasted. They found that the condition of the net was tied to the household's habits and circumstances. Nets in homes with older heads of the household tended to last longer, as did nets in wealthier families. The presence of young children in the home was linked to faster wear and tear, likely because the nets were handled more frequently. How the nets were cared for mattered immensely. Families that folded their nets when they were not in use, rather than leaving them hanging loosely, saw their nets last longer. Similarly, drying nets on bushes or fences after washing caused more damage than drying them in other ways. Cooking inside the room where the net was hung also accelerated damage, likely due to smoke and heat. Perhaps most importantly, households that received clear messages about how to care for their nets were more likely to keep them in good condition for a longer time.

The study concluded that while some nets can last longer than the traditional three-year expectation, others fail much sooner, and the chemical protection fades regardless of the brand. The findings suggest that health programs cannot simply distribute nets and assume they will work for a set number of years. Instead, the timing of replacement campaigns must be tailored to the specific durability of the net type being used and the local conditions. In areas where nets like the ones in Burera are used, a three-year replacement cycle might be too long, leaving people unprotected. The research highlights that improving how people care for their nets through education and behavior change could extend their life, but it also underscores the need for continuous monitoring to ensure that the tools being used are still doing their job before the next distribution cycle begins.