Impact of seasonal malaria chemoprevention: a plausibility evaluation of routine data from health facilities in three implementing states in Nigeria

Background Seasonal malaria chemoprevention (SMC) has been recommended by the World Health Organization since 2012 for children aged 3–59 months in areas where malaria transmission is highly seasonal. By 2024, SMC had been successfully implemented in all 21 eligible states in Nigeria. Given this widespread implementation, there has been increasing interest in understanding the impact of the intervention under programmatic conditions. This study assessed changes in malaria incidence and related epidemiological outcomes among the target population of children in three SMC implementing states in Nigeria. Methods A pre-post study plausibility evaluation design was used for this study. Data from routine health management information systems were extracted from selected health facilities to compare the incidence of parasitologically-confirmed uncomplicated malaria cases and secondary outcomes among children aged 3–59 months within the catchment populations of those health facilities. Mixed-effects, multilevel, negative binomial regression models were employed to estimate the impact of SMC on outcomes of interest between the pre-SMC period (2021) and SMC period (2022). Results Data were collected in 36 health facilities: 12 each in Kogi state, Oyo state, and the Federal Capital Territory. The mean incidence of uncomplicated malaria was 20 cases per 1000 children aged 3–59 months in 2021, and 9 cases per 1000 children in 2022. After accounting for potential confounders, malaria incidence was 50% (95% confidence interval [CI]: 39–60) lower in the SMC period compared with the pre-SMC period (adjusted incidence rate ratio (IRR): 0.50, 95% CI: 0.40–0.61, p < 0.001), with notable variations in the level of reduction across the three study locations. Incidence of all-cause fever per 1000 children was 29% (95% CI: 14–41) lower in 2022 compared with 2021 (adjusted IRR: 0.71, 95% CI: 0.59–0.86, p < 0.001). Observed levels of severe malaria and attributable deaths were too low to measure the impact of SMC on those outcomes. Conclusion The study found significantly lower levels of incidence of uncomplicated malaria following the introduction of SMC. It thus provides evidence on the potential impact of the intervention in real-world settings while underscoring the need for further improvement to and utilisation of routine data to monitor impact in eligible settings.