Clara Champagne

Background: Insecticide-treated nets (ITNs) are a cornerstone of malaria prevention. Increasing insecticide resistance has reduced the effectiveness of pyrethroid-only (PYR) ITNs. Chlorfenapyr-pyrethroid insecticide-treated nets (CFP-PYR-ITNs) offer higher efficacy but at a higher cost. Under budget constraints, this could result in fewer ITNs being distributed or less frequent distributions, and it is unclear how this would affect the malaria burden.Methods: We used an individual-based model of malaria transmission to compare the impact on malaria cases of deploying PYR-ITNs via mass distribution versus CFP-PYR-ITNs with no compromise or reduced (25% or 50%) coverage or deployment frequency (every four or six years) in areas with high PY resistance. ITN effects on Anopheles mosquitoes were previously parameterised to entomological studies and clinical trials.Findings: Deploying CFP-PYR-ITNs at high coverage every three years provided the greatest protection. CFP-PYR-ITNs remained more effective than PYR-ITNs even when CFP-PYR-ITN coverage or deployment frequency was substantially reduced (25%) in settings with PYR resistance. Reducing deployment frequency was more effective when ITNs maintained protection between distributions. In contrast, when ITN retention was short, reducing coverage was more advantageous as it prevented a malaria rebound between distributions. Under reduced-coverage scenarios, individuals who would lose ITN access still benefited from the switch to CFP-PYR-ITNs due to their stronger community protection.Interpretation: If budget constraints necessitate deploying CFP-PYR-ITNS at lower coverage or frequency than PYR-ITNs, CFP-PYR-ITNs would still provide greater protection against malaria than PYR-ITNs to the whole population in settings with PYR resistance.

Insecticide-treated nets (ITNs) are the primary malaria vector control intervention in Benin, yet their real-world protective impact is shaped by operational and behavioral factors that extend beyond what is captured in controlled experimental settings. This modeling study aimed to quantify the successive losses in ITN protection by adapting a cascade of effectiveness framework to the specific epidemiological context of Benin, enabling a direct comparison of various WHO-prequalified ITNs under realistic field conditions. Entomological data from four experimental hut trials conducted in Covè, southern Benin, were integrated with Benin-specific behavioral and operational parameters, including net physical attrition, ITN usage and in-bed exposure, to sequentially quantify the impact of each real-world constraint on operational effectiveness. Across all net types, operational effectiveness was substantially lower than entomological efficacy alone, with cumulative losses of 40 to 60 percentage points from theoretical maximum protection. Net physical attrition and usage consistently emerged as the dominant drivers of this decline. Among the ITNs considered, chlorfenapyr-pyrethroid ITNs demonstrated the highest final operational effectiveness (52–66%). These findings demonstrate that physical durability and consistent usage are as critical as insecticidal potency in determining ITN operational effectiveness, with direct implications for procurement and deployment decisions in Benin and comparable settings.

Background: The malaria transmission potential and the vulnerability of Anopheles mosquitoes to different vector control methods depend, among other factors, on the endophily, endophagy, anthropophagy and survival of each species. Local information on these bionomic parameters is generally unavailable. Methods: To address this, we estimated species-specific values of these parameters using an augmented version of the global database of bionomics data by Massey et al. (2016). We applied inclusion and exclusion criteria to select eligible studies with relevant experimental designs that minimise bias from collection methods for parous, sac, endophagy, and endophily rates as well as for the resting duration. For the human blood index (HBI), we separated data from indoor and outdoor collections. We fitted hierarchical Bayesian models with levels based on Anopheles taxonomy to estimate these quantities. Based on the estimated bionomics, we quantified the expected vectorial capacity reduction after the introduction of a pyrethroid-pyrrole insecticide-treated net (ITN) for 57 Anopheles species. Results: We identified 26 eligible studies for endophagy and 61 for the parous rate, leading to a Bayesian posterior average for the Anopheles genus of 42% (95% credible interval: 18-70) and 55% (32-77) respectively. HBI values widely varied depending on the location of collection, except for some species showing strong anthropophilic behaviours. Resting duration was estimated to be 2.1 days (1.2 – 4.8) at the genus level. Few studies were available to estimate the sac and endophily rates, which prevented us from deriving precise estimates for the whole Anopheles genus. Our estimates of the vectorial capacity reduction following the introduction of a pyrrole-pyrethroid ITN ranged between 48% and 76% across species, highlighting the important differences among mosquito species in vulnerability to vector control interventions. Conclusion: This work demonstrates how data from both Anopheles species complexes and individual species can be leveraged to generate species-specific estimates of bionomic parameters, capturing the local characteristics and behaviour of malaria vectors. The dataset is readily updatable as new data become available. However, more frequent and standardised field surveys are still needed to accurately characterise local vector behaviour.

As insecticide resistance spreads in Africa, next-generation insecticide-treated nets (ITNs) are increasingly being deployed to protect vulnerable populations against malaria. While these nets provide greater entomological efficacy against resistant mosquitoes, their effectiveness against malaria transmission also depends on other factors, such as durability, access, usage, and activity patterns of hosts and vectors. Here, we quantify the impact of two next-generation ITNs, namely Interceptor®G2 (chlorfenapyr-pyrethroid) and Olyset® Plus (piperonyl butoxide-pyrethroid), in a cascade from entomological efficacy to population-level effectiveness. We use a mathematical model that we parameterize with entomological data and validate against results from randomized controlled trials. We found that, beyond entomological factors, operational factors including functional survival, ITN use and in-bed exposure critically impact ITN effectiveness overall and per ITN types. Our results obtained for Tanzania can be extended to other contexts in a dashboard allowing users to explore product selection based on setting-specific factors that influence ITN effectiveness.

As insecticide resistance spreads in Africa, new-generation insecticide-treated nets (ITNs) are increasingly being deployed to protect vulnerable populations against malaria. While these nets provide greater entomological efficacy against resistant mosquitoes, their effectiveness against malaria transmission also depends on other factors, such as durability, access, usage, and activity patterns of hosts and vectors. Here, we quantify the impact of two new-generation ITNs, namely Interceptor®G2 (chlorfenapyr-pyrethroid) and Olyset®Plus (piperonyl butoxide-pyrethroid), in a cascade from entomological efficacy to population-level effectiveness. We use a mathematical model that we parameterize with entomological data and validate against results from randomized controlled trials. We found that, beyond entomological factors, operational factors including functional survival, ITN use and in-bed exposure critically impact ITN effectiveness overall and per ITN types. Our results obtained for Tanzania can be extended to other contexts in a dashboard ( https://aimswisstph.shinyapps.io/ITNcascadesdashboard ) allowing users to explore product selection based on setting-specific factors that influence ITN effectiveness.

Background Seasonal malaria chemoprevention (SMC) has been implemented yearly in northern Benin since 2019 to reduce the malaria burden in children under 5 years of age. Its geographic scope was progressively extended until in 2022 two different extensions of SMC were considered: either demographic - children aged 5 to 10 in the currently targeted departments would also receive SMC, or geographic to children under 5 in new eligible departments to the south. As SMC had neither been implemented in the areas nor age groups suggested for expansion, modelling was used to compare the likely impact of both extensions. Methods The model OpenMalaria was calibrated to represent the history of malaria interventions and transmission risk in Benin. Currently planned future interventions and two scenarios for SMC extensions were simulated to inform where impact would be the highest. Results The model predicted that between 2024 and 2026 the geographic extension of SMC would avert at least four times more severe malaria cases and five times more direct malaria deaths per targeted child than the demographic extension. However, numbers of severe cases averted per targeted child were similar between health zones eligible for geographic extension. Conclusions The geographic extension is more impactful and likely more cost-effective than the demographic extension, and will be implemented from 2024. Health zones were prioritised by availability of community health workers to deliver SMC. Mathematical modelling was a supportive tool to understand the relative impact of the different proposed SMC extensions and contributed to the decision-making process. Its integration significantly enhanced the utilisation of data for decision-making purposes. Rather than being used for forecasting, the model provided qualitative guidance that complemented other types of evidence.

In order to evaluate the impact of various intervention strategies on Plasmodium vivax dynamics, we introduce a simple mathematical model that can be easily adapted to country-specific data. The model includes case management, vector control, mass drug administration and reactive case detection interventions and is implemented in both deterministic and stochastic frameworks. It is available as an R package to enable users to calibrate and simulate it with their own data. By simulating and comparing the impact of various intervention combinations on malaria risk and burden, this model can a useful tool for strategic planning, implementation and resource mobilization.

The national deployment of polyvalent community health workers (CHWs) is a constitutive part of the strategy initiated by the Ministry of Health to accelerate efforts towards universal health coverage in Haiti. Its implementation requires the planning of future recruitment and deployment activities for which mathematical modelling tools can provide useful support by exploring optimised placement scenarios based on access to care and population distribution. We combined existing gridded estimates of population and travel times with optimisation methods to derive theoretical CHW geographical placement scenarios including constraints on walking time and the number of people served per CHW. Four national-scale scenarios that align with total numbers of existing CHWs and that ensure that the walking time for each CHW does not exceed a predefined threshold are compared. The first scenario accounts for population distribution in rural and urban areas only, while the other three also incorporate in different ways the proximity of existing health centres. Comparing these scenarios to the current distribution, insufficient number of CHWs is systematically identified in several departments and gaps in access to health care are identified within all departments. These results highlight current suboptimal distribution of CHWs and emphasize the need to consider an optimal (re-)allocation.