Assessing the effectiveness of seasonal malaria chemoprevention on malaria burden among children under 5 in northern Benin: a statistical modelling approach

Introduction: Children under 5 in northern Benin remain highly vulnerable to malaria infection. Seasonal malaria chemoprevention (SMC), implemented since 2019, shows promise in reducing this burden. However, current malaria funding cuts threaten its future implementation putting additional children's lives at risk. Generating evidence about SMC's effectiveness is therefore crucial to support continued implementation. Methods: A quasi-experimental analysis evaluated SMC's impact on malaria morbidity in children under 5 during 2019-2022. Routine malaria indicators retrieved from the Health Management Information System from six SMC-treated health zones (HZs) were compared against synthetic counterfactuals constructed using nine eligibles untreated HZs. Synthetic control methods identified control HZs best matching intervention HZs on pre-intervention (2017-2018) characteristics (rainfall, temperature, relative humidity), with pre-intervention fit assessed using root mean square prediction error. Generalised linear mixed models then estimated SMC effects on uncomplicated and severe malaria incidences, accounting for reporting bias, other interventions and key environmental factors. Results: Following SMC implementation, severe malaria incidence decreased by 41% in the intervention group (incidence rate ratio (IRR): 0.59, 95% CI 0.44 to 0.79) but increased by 26% in the control group (IRR: 1.30, 95% CI 0.97 to 1.63). Although uncomplicated malaria incidence rose in both groups, the increase was significantly lower in the SMC group (2.49%) compared with the control (16.3%). The ratio of IRR in the intervention versus control HZs was 78% (95% CI 63% to 96%, p=0.004) for uncomplicated malaria and 47% (95% CI 30% to 74%, p