In the DHA-PQ group only, a subset of 210 children will be asked to provide finger prick blood samples for PK analysis on day 0, between day 0 and day 6, on day 7, and between day 8 and day 30. To calibrate measurements of drug concentration in peripheral blood against existing PK models, each month 17 of these children will be asked to also provide a venous sample (up to 2ml taken into a vacutainer) on three occasions (one between day 0 and 6, one on day 7, and one between day 8 and 30). In addition, a separate group of 750 children aged 3 to 59 months will be recruited to be surveyed at the end of the transmission season to determine the prevalence of malaria parasitaemia and of drug-resistance parasite genotypes in the study area.