In order to understand the relationship between level of drug resistance and long terms effects of IPTi, the exact level of drug resistance in the IPTi target infants needs to be established and related to IPTi efficacy. Thus a modified WHO in vivo drug resistance study in 2-10 month old asymptomatic infants needs to be conducted as part of the Kilimanjaro IPTi study and a comparison made with the efficacy of SP estimated from a standard WHO 6-59 month WHO in vivo efficacy study.