It is expected that first line antimalarial drug policy will change in November 2006 from SP to lumefantrine/arthemeter. After this date it will not be ethical to continue the 6-59 month study in symptomatic children. However for the asymptomatic children it will be ethical to continue as SP use continues in asymptomatic women for IPTp and if adopted as a strategy for Tanzania, SP will be used for IPTi. Therefore we plan to carry out the SP efficacy in 6-59 month study in symptomatic children as soon as possible and if the national policy changes before completion of the study we will have to halt it. The 2-10 month old asymptomatic study will run concurrently until completion.