 The RTS,SAS01E candidate malaria vaccine is being developed for the routine immunization of infants and children living in malaria-endemic areas as part of the Expanded Program of Immunization EPI. 30 efficacy against clinical malaria and 58 efficacy against severe malaria disease was seen with a related vaccine, RTS,SAS02A, in children aged 1 to 4 years Malaria-026 in Mozambique. The efficacy against clinical malaria and infection was sustained beyond 18 months. The RTS,SAS01 vaccines have been developed in parallel with the RTS,SAS02 vaccines, and differ in the adjuvant formulation which has been shown to be more immunogenic.The utility of a partially effective vaccination depends heavily on the overall effect of malaria incidence during a childs acquisition of natural immunity. However, other cohorts vaccinated in Phase II studies have already discontinued follow up for episodes of malaria, and the planned Phase III studies will run for at most 30 months post vaccination. The proposed extended follow up is expected to run for four years and will inform the design of Phase 4 studies and may prove critical in informing public health policy once the vaccine is licensed. 