Household-level effects of seasonal malaria chemoprevention in the Gambia

Abstract

Abstract In 2022 the WHO recommended the discretionary expansion of the eligible age range for seasonal malaria chemoprevention to children older than 4 years. Older children are at lower risk of clinical disease and severe malaria so there has been uncertainty about the cost benefit for national control programmes. However a growing body of laboratory research suggests school-age children are the majority contributors to the infectious reservoir for malaria, and extended age SMC programmes may have significant impacts on malaria transmission. Evidence for this effect in routinely implemented SMC programmes at scale is limited. In 2021 the Gambia extended the eligible age range for SMC to 9 years. We use a household-level mixed modelling approach in a population cohort covering 2210 inhabitants of 10 communities in the Upper River Region to demonstrate the hazard of clinical malaria in older participants aged 10 + years ineligible for SMC decreases by 20% for each additional SMC round per child 0–9 years in the same household. Older inhabitants also benefitted from reduced risk of asymptomatic infections in high SMC coverage households. We assessed these effects for spatial autoregression and showed that impacts are highly localised, with no detectable spillover from nearby households.