Last month, the World Health Organization (WHO) updated its Guidelines for Malaria, recommending the use of a new class of mosquito net, containing two active ingredients to kill and repel malaria-transmitting mosquitoes in areas where they have developed resistance to pyrethroids.
Malaria infects around 247 million people each year, with children and pregnant women most at risk of serious infection and death. In 2021, around 80 percent of the hundreds of thousands of malaria deaths occurred in under-fives, with most of the remaining deaths occurring in children under 10 and pregnant women.
Insecticide treated nets (ITNs) are an effective means of malaria prevention that protect household members from being bitten by mosquitoes carrying malaria while they sleep. Since synthetic pyrethroids were incorporated into bednets as Insecticide Treated Nets (ITNs) and sprayed onto the walls of domestic dwellings as Indoor Residual Spraying (IRS), they have significantly contributed to averting malaria morbidity and mortality. The scale of ITN deployment in sub-Saharan Africa is estimated at 1.9 billion ITNs between 2004 and 2019.
However, since 2015, the downward trend of malaria case numbers has plateaued. A contributing factor in this stalled progress has been attributed to the malaria mosquitoes developing genetic modifications enabling them to become resistant to the toxic effects of pyrethroids.
In response, WHO has recommended that nets treated with two new classes of dual ingredient – pyrethroid-chlorfenapyr and pyrethroid-pyriproxyfen – can be deployed in areas with pyrethroid resistance, instead of pyrethroid-only nets. Using two active ingredients decreases the likelihood of mosquitoes being resistant to both. However, as these new dual active ingredient nets would require extra resources to purchase, their cost-effectiveness may impact upon coverage and equity.
As part of a three-year research project in Ondo and Anambra states in Nigeria, Malaria Consortium is assessing the impact of mass ITN campaigns to reduce malaria incidence when deployed alongside other proven malaria control interventions. The study seeks to improve vector control decisions and better understand the cost-effectiveness of ITNs containing both pyrethroids and the efficacy-enhancing synergist piperonyl butoxide (PBO).
The WHO’s latest recommendations follow results from randomised control trials in Africa. Alongside the new recommendations, WHO has also published new guidance for national malaria programmes on the prioritisation of ITNs in situations where resources are limited.