Field trials of an asexual blood stage malaria vaccine: studies of the synthetic peptide polymer SPf66 in Thailand and the analytic plan for a phase IIb efficacy study. by Ballou, W, Blood, J, Chongsuphajaissidhi, T, Gordon, D, Heppner, D, Kyle, D, Luxemburger, C, Nosten, F, Sadoff, J, Singhasivanon, P