Remarks The conditionality of this recommendation is driven by the current higher unit cost of pyrethroid-PBO ITNs compared to pyrethroid-only LLINs and therefore the uncertainty of their affordability in different settings. Furthermore, as PBO is less washresistant than pyrethroids, its bioavailability declines faster over the three-year estimated life of an ITN; therefore, the added impact of pyrethroid-PBO ITNs over that of pyrethroid-only LLINs may decline over time. The evidence comes from two sites in eastern Africa with pyrethroid resistance and not from other geographies where transmission levels and vector characteristics may vary. PBO acts by inhibiting certain metabolic enzymes, primarily oxidases, and so are likely to provide greater protection than pyrethroid-only LLINs where mosquitoes display mono-oxygenase-based insecticide resistance mechanisms. In deciding whether pyrethroid-PBO ITNs may be appropriate in their context, malaria programmes should:

• consider the deployment of pyrethroid-PBO ITNs in areas where resistance to pyrethroids in local vectors has been detected;
• determine whether resources are adequate to cover the extra cost of pyrethroid-PBO ITNs, while ensuring that coverage of populations at risk of malaria is not affected;
• note that WHO recommends that ITNs prequalified by WHO be selected for deployment.

Practical info Given that the evidence indicates that unwashed pyrethroid‐PBO ITNs are more effective than pyrethroid-only LLINs in areas with pyrethroid resistance up to 25 months post-deployment, the decision on whether to switch from pyrethroid-only LLINs to pyrethroid-PBO ITNs, or another ITN product designed to provide enhanced efficacy in areas of pyrethroid resistance, should be guided by resource availability. WHO recommends that pyrethroid‐PBO ITNs be used where pyrethroid resistance is confirmed using standard procedures [22]. Given that pyrethroid‐PBO nets are designed to provide improved impact against resistant mosquitoes in which pyrethroid resistance is, at least in part, conferred by a monooxygenase-based resistance mechanism, determining the presence of such resistance mechanisms in local vector populations will provide additional information to help target deployment. In deciding whether to use potentially more expensive pyrethroid-PBO ITNs, malaria programmes should consider the impact this switch may have on vector control coverage. Deployment of pyrethroid-PBO ITNs must only be considered in situations where coverage with effective vector control (primarily ITNs or IRS) will not be reduced. The primary goal must be to ensure continued access and use of ITNs or IRS at levels that ensure optimal coverage for all people at risk of malaria as part of an intervention package. Post-distribution monitoring of nets to estimate coverage in terms of access to and use of nets and other malaria interventions is recommended. Pyrethroid-PBO ITNs should not be considered a tool that can alone effectively manage insecticide resistance in malaria vectors. Despite the recent recommendation of other ITN classes and associate product, the development and evaluation of ITNs treated with non-pyrethroid insecticides and other innovative vector control interventions for deployment across all settings continues to remain a priority to provide alternatives for use in a comprehensive IRM strategy. The systematic review reported that the washing of pyrethroid‐PBO ITNs may result in lower mosquito mortality and higher bloodfeeding success than the washing of pyrethroid-only LLINs. The durability of pyrethroid‐PBO ITNs compared to pyrethroid-only LLINs has been questioned previously based on wash-resistance data. The added epidemiological and entomological impact of pyrethroid-PBO ITNs depends on the bioavailability and retention of PBO on/in the net. If this is reduced significantly over time and/or declines with washing, the greater impact of pyrethroid-PBO ITNs over pyrethroid-only LLINs in terms of protection against malaria may be limited to less than three years. As part of M&E activities, data collected by programmes on net durability would provide information on the life span of pyrethroid-PBO ITNs under field conditions and hence on the period over which the additional impact is maintained. Programmes that decide to switch from pyrethroid-only LLINs to pyrethroid-PBO ITNs based on concerns regarding continued effectiveness and/or insecticide resistance status of local vectors, should not revert back to the use of pyrethroid-only LLINs thereafter. Instead, programmes should plan for continued deployment of pyrethroid-PBO ITNs in that geographic area or develop plans for deployment of other equally or more effective new interventions once these are covered by a WHO recommendation.