This is a two-arm, cluster-randomised, phase IV trial conducted in Chad to assess theprotective efficacy and impact in real-life conditions of a new strategy foradministering the R21/MM malaria vaccine, synchronized within a seasonal malariachemoprevention (SMC) campaign, among children living in areas of high seasonal malariatransmission.In this study, a cluster is defined as the catchment area of a primary care healthcentre. In Chad, each catchment area is known as a 'zone of responsibility' (French: Zonede Responsibilité' [ZR]).Twenty-six (26) of the total 27 ZRs in the districts of Moïssala and Dembo will berandomized in a 1:1 ratio to receive a 4-dose (3 primary doses + 1 booster) R21/MMschedule either (1) integrated into the routine EPI vaccination program (the "Routine"control arm), or (2) synchronized with an annual seasonal malaria chemoprevention (SMC)campaign (the "Synchronized" intervention arm).Malaria incidence: R21/MM effectiveness will be assessed using the incidence ofbiologically confirmed clinical malaria (trial primary endpoint). The incidence ofclinical malaria will be determined through enhanced surveillance of malaria cases inhealth centres and hospitals over a 17-month period (August 2025 - December 2026).Coverage surveys: Cross-sectional surveys (cluster sampling) will be carried out tomeasure R21/MM vaccine coverage, SMC coverage, coverage of other malaria preventionmeasures, and coverage of other EPI vaccines.Nested case-control study: A sub-sample of children admitted to Moïssala DistrictHospital with severe clinical malaria will be offered the opportunity to participate in anested case-control study designed to estimate the individual protective efficacy ofR21/MM against severe malaria.