This is a cluster randomized trial to determine the impact of seasonal R21/MM mass vaccination (all ages) on malaria transmission and morbidity. Fifty-four villages (30 in The Gambia and 24 in Burkina Faso) will be randomized to either mass vaccination with R21 or no mass vaccination. The primary objective is to compare in intervention and control clusters the prevalence of malaria (all age groups) at peak transmission after seasonal mass vaccination with R21 (3 monthly doses). Secondary objectives are: 1. To assess the safety and tolerability of R21 through spontaneously reported adverse events. 2. To compare in intervention and control clusters the incidence of malaria infection (all age groups) during the malaria transmission season following seasonal mass vaccination with R21 (3 monthly doses). 3. To compare in intervention and control clusters the incidence of clinical malaria (all age groups) after seasonal mass vaccination with R21 (3 monthly doses). 4. To compare in intervention and control clusters the prevalence of malaria (all age groups) at peak transmission after one booster dose of R21. 5. To compare in intervention and control clusters the incidence of malaria infection (all age groups) during the malaria transmission season following one booster dose of R21. 6. To compare in intervention and control clusters the incidence of clinical malaria (all age groups), after one booster dose of R21. 7. To determine the coverage of seasonal mass vaccination with R21 (primary series of three vaccinations and booster) in intervention clusters and related socio-cultural factors 8. To estimate the cost of seasonal mass vaccination with R21 administration. 9. To estimate the cost-effectiveness of seasonal mass vaccination with R21 compared to standard malaria control measures. The exploratory objective is to determine whether serological markers can detect changes in malaria transmission following mass vaccination with R21.