Estimating the Malaria Prevention Impact of New Nets: Observational Analyses to Evaluate the Evidence Generated During Piloted New Net Distributions in Mozambique

The World Health Organization's (WHO) 2018 World Malaria Report estimates that in 2017, 219 million cases of malaria occurred worldwide resulting in 435,000 deaths, 93% of which occurred in Africa (WHO 2018). While this represents a remarkable improvement in comparison with 2000, with malaria deaths having fallen by 40% in Africa, the downward trends in incidence and mortality stalled between 2015 and 2017. This recent failure to maintain the hard-won progress, let alone accelerate progress towards elimination, over the past three years has caused WHO to describe the global fight against malaria as being at a crossroads, calling for increased funding and highlighting the need to develop, optimize, and implement new tools to combat malaria.

Universal coverage of populations at risk with malaria vector control interventions, primarily insecticide treated nets (ITNs) and indoor residual spraying (IRS), in malaria-endemic countries is a global and national priority because of its fundamental importance for malaria control and elimination. Unfortunately, the effectiveness of these tools is threatened by the emergence and spread of pyrethroid resistance in key mosquito populations, which is now reported in more than 85% of all malaria endemic countries and poses significant risk to the future impact of these tools. Emerging evidence suggests, however, that increasing mosquito mortality and thereby continuing to reduce malaria transmission is possible in areas with pyrethroid resistance by introducing new insecticide formulations for IRS and ITNs. For example, Protopopoff et al. showed in Tanzania that the distribution of LLINs with piperonyl butoxide (PBO) plus pyrethroid reduced malaria prevalence by 13% compared to standard pyrethroid-only LLIN distribution (42% vs. 29%; p=0.0011), and Tiono et al., working in Burkina Faso, showed that the distribution of a dual active-ingredient ITN reduced clinical malaria incidence by 22% (Incidence Rate Ratio = 0.88; p=0.04) and potentially infective mosquito bites by 51% (entomological inoculation rate ratio = 0.49; p<0.0001) compared to the distribution of a standard pyrethroid-only LLIN.

While there is evidence that standard LLINs can continue to provide effective personal protection to regular net users in regions with resistant vector populations, new classes of ITNs developed to perform against pyrethroid-resistant mosquitoes have been developed, with early trials and modelling suggesting that they may provide superior protective efficacy against malaria in areas with pyrethroid-resistant vectors. Access to these new resistance-breaking ITNs is restricted by need for efficacy data for continuing policy recommendations, high prices, lack of evidence of cost effectiveness compared to pyrethroid-only LLINs, and consequent poor demand in an uncertain market. Two types of next-generation ITNs, each utilizing a different mixture of active ingredients from different insecticide classes, have recently received WHO prequalification listing demonstrating that they perform to the thresholds required of pyrethroid-only ITNs and have no known specific side effects: Interceptor G2® (IG2; by BASF SE) and Royal Guard®(RG; by Disease Control Technologies, LLC). The IG2 ITN contains a mixture of a pyrethroid (alpha-cypermethrin) and a pyrrole (chlorfenapyr), while the RG ITN contains a mixture of the same pyrethroid (alpha-cypermethrin) and an insect growth regulator (pyriproxyfen). While both net types have been subsequently registered and approved for use in Mozambique based on this WHO listing, the Roll Back Malaria Vector Control Advisory Group guidance indicates that dual active ingredient ITNs will require further epidemiological evidence before policy recommendations are made for their use in preference to pyrethroid-only ITNs in certain settings.

The Global Fund and Unitaid have developed a market shaping program for next-generation ITNs with novel insecticide formulations. Evidence on the efficacy of IG2 and RG ITNs will be generated by the project through two randomized control trials taking place in Benin and Tanzania. In addition, through this program, these next-generation ITNs will be made available to countries for incorporation into their national distribution programs as pilot distributions with the aim of determining real-world effectiveness and cost-effectiveness in different contexts. In addition to the pilot distribution of IG2s taking place in Mozambique, three other countries will be piloting next-generation ITNs as part of the New Nets project: Burkina Faso, Nigeria, and Rwanda. This research will utilize these pilot distributions to understand the cost-effectiveness of the new ITNs in the chosen settings. The NMCP in Mozambique, in discussion with the Global Fund, chose to incorporate IG2, RG, and PBO ITNs into the 2020 mass distribution campaign. This study will collect information to determine the public health impact of the RG, PBO, and IG2 ITNs in Mozambique, in comparison to two sites that will receive standard pyrethroid-only ITNs. The aim of this research is to better understand the effectiveness and cost effectiveness of IG2 and RG ITNs in Mozambique and to collect data on community uptake of the ITNs.

During the upcoming pilot implementation enhanced entomological, epidemiological, and net use data will be collected in up to six study districts: two districts receiving the dual-active ingredient ITN Interceptor® G2 (BASF: alphacypermethrin + chlorfenapyr); one district that will receive the dual-active ingredient ITN Royal Guard® (Disease Control Technologies: alphacypermethrin + pyriproxyfen); one district receiving an ITN containing an insecticide plus an insecticide synergist, Olyset®Plus (Sumitomo Chemical: permethrin + piperonyl butoxide); and two districts receiving the standard pyrethroid-only ITNs DuraNet® (Shobikaa Impex Private Limited: alphacypermethrin). Data will be analyzed and results disseminated to support the NMCP, donors, policymakers, and other national and regional stakeholders in their ITN decision-making and planning processes. Each component aims specifically to:

• Epidemiological component - measure the epidemiological impact of the new IG2 ITNs, Royal Guard ITNs, PBO ITNs, and standard ITNs in real deployment scenarios through observational studies. These studies will compare trends in (1) malaria case incidence rates passively reported to the national health system (passive case detection (PCD)) and (2) malaria infection prevalence, measured through rapid diagnostic tests (RDTs), in children aged 6 months to 5 years of age from annual cross-sectional surveys during peak transmission periods.
• Entomological component - evaluate the impact of the different net types on vector populations and biting rates, compared to standard ITNs, through mosquito surveillance data that will measure trends in species-specific (1) adult vector densities (2) indoor and outdoor human landing rates (3) estimated entomological inoculation rates and (4) insecticide resistance patterns. These entomological surveillance activities are aligned with NMCP activities and are not part of the human subject research component of this study.
• Anthropological component - map patterns of ITN usage to determine transmission risk defined as the intersection between time at risk of mosquito blood feeding and human activities not under protection of an ITN, through gathering evidence on ITN uptake and usage. The collection of reliable data on such patterns, both indoors and outdoors, becomes thus an essential component of the evaluation of the ITN pilots for both modeling and contextual analysis of impact.
• Durability monitoring - monitoring of standard, IG2, RG and PBO ITNs in one district each, prospectively measuring physical durability, attrition, and chemical durability.
• Costing and cost-effectiveness component - estimate the cost and cost-effectiveness of IG2, RG and PBO ITNs in Mozambique through data on the price of the product, delivery and deployment costs, and product effectiveness based on case incidence rates measured during the epidemiological component of this study. Additionally, mean costs per case averted that might occur in other contexts will be modeled and incorporated into the cost-effectiveness evaluations.