The main objective of this component of the drug resistance study is to understand the relationship between the efficacy of antimalarial drugs used for IPTi and the long term effect of IPTi on incidence of clinical malaria. Schellenberg et al (2005). observed a 36% reduction in the incidence of clinical malaria in the second year of life in the SP IPTi group compared to the placebo group even though the last course of SP IPTi was given at 9 months of age (Schellenberg et al, 2005). This suggests that SP IPTi in an area with moderate malaria transmission and moderate levels of resistance to SP (+/-25%) IPTi may enhance the development of immunity against malaria. In contrast, a study in Ghana in area with very high and seasonal malaria transmission and very low resistance to SP (<10%) showed a 20% increase in the incidence of clinical malaria with high parasite density (>5000 parasites/ml) in SP IPTi group compared to placebo group. The nature of the relationship between drug resistance and the long term effect of IPTi on malaria remains unclear.