The World Health Organization has issued a new recommendation supporting the use of spatial repellents, the first new class of malaria vector control agent in decades to be endorsed for slowing the spread of the mosquito-borne disease.
Spatial repellents, also known as spatial emanators, emit mosquito-killing chemicals into the air, discouraging them from entering treated spaces, thereby preventing them from locating and biting human hosts. The products, including a one-month and a 12-month version, are designed to hang indoors, on walls in places where malaria is endemic.
WHO’s new recommendation is largely based on research funded by Unitaid under the Advancing Evidence for the Global Implementation of Spatial Repellents (AEGIS) project. The Johns Hopkins Center for Communication Programs has steered the social science research for the five-year project, which is led by the University of Notre Dame.
CCP’s Sean Blaufuss, who has worked on the AEGIS project, says the WHO announcement comes at a crucial moment when malaria cases have been on the rise and health officials are looking for complementary low-cost mosquito control tools to use alongside the proven strategies of distributing insecticide-treated bed nets and the employing indoor residual spraying.
“This is a huge step toward having another tool in the fight against mosquito-borne diseases including malaria,” Blaufuss says. “This should unlock additional options for countries to use spatial emanators as a complementary tool to increase the pressure on these diseases.”
Unlike nets, spatial repellents may provide an added layer of protection against day-time mosquito biting, when residents of a household are active within the home and not sleeping under a net. The repellants are also a low-cost product that can enhance other malaria safeguards already in place.
“This recommendation opens the door to a new intervention for national malaria control programs at a time when innovation is urgently needed,” Daniel Ngamije, MD who directs the Global Malaria Program at WHO, announced Wednesday. “As rising insecticide resistance and changes in mosquito behavior threaten the effectiveness of long-standing vector control tools, spatial emanators offer an innovative approach to help protect people at risk from infection.”
In January, AEGIS researchers publishing in The Lancet, found that Mosquito Shield™, a special repellent made with the insecticide transfluthrin, reduced malaria infections in Busia County, Kenya by 33.4 percent during interim analysis and 32.7 percent by the end of the study, among children aged 6 months to 10 years.
In July, AEGIS researchers, including several from CCP and the Kenya Medical Research Institute, published findings in Malaria Journal about how the communities where spatial repellents were deployed felt about them.
They followed up several times with cohorts of residents in Busia County who had been given the repellents. In this study, the researchers replaced the repellents every 28 days and conducted follow-up interviews with users five times over an 18-month period, said CCP’s Samantha Tsang, who was the team lead for CCP’s work on AEGIS.
Through a modified trials of improved practices study (TIPS), the social science team found that participants in the intervention group continuously felt like the Mosquito Shield™ provided protection from mosquitos, whereas participants from the control group (people who did received a placebo repellent) reported a decline in perceived efficacy over time.
The TIPs approach also provided practical solutions to researchers, such as using hooks instead of tape for installation and positioning hooks sideways to prevent repellents from falling off the walls due to drafts.
One important piece to consider before implementation: Tsang and her colleagues found that some participants stopped using their bed nets after the installation of the repellents, which could put people more at risk for malaria. Tsang says there needs to be strong community engagement and tailored messaging created for people to understand repellents aren’t replacements for bed nets, but are meant to be used alongside other mosquito control products.
“I think as we move forward, it will be interesting and important to explore 1) how do we ensure spatial emanators are used as a complementary, not replacement, mosquito control product by the end user; 2) what are the most effective ways to distribute spatial emanators in order to ensure optimal and correct use; and 3) how do we encourage proper disposal of spatial emanators to reduce the environmental impact of these products,” Tsang says.
As part of its recommendations, WHO also prequalified two spatial emanators products, Mosquito Shield™ and Guardian, manufactured by SC Johnson & Son, Inc. This means that spatial repellents will become accessible through funders and in the market in the coming years.
While the conditional recommendation marks a major step forward, according to the WHO, “key evidence gaps remain – particularly around the effectiveness of spatial emanators when used alone, their potential to protect people outdoors or in humanitarian emergencies, and their role in managing insecticide resistance. Global research and funding partners are now working to close these gaps and strengthen the evidence base for spatial emanators.”
At the same time as the WHO announcement, Unitaid revealed that it would make another $18 million investment to explore these questions in Cameroon.
As part of AEGIS, Tsang and Blaufuss have also conducted research on spatial repellents in Sri Lanka, focusing on the reduction of dengue cases.
