Subsequently, the shortest efficacious regimen (V1) and a three-dose regimen (Day 0, 7 and 28) of the highest safe dose (V2) will be selected and verified against placebo (normal saline (NS)). Groups V1 and V2 will be vaccinated at approximately the same time and undergo repeat CHMI three and eight weeks after the last immunization. Volunteers will either receive PfSPZ Vaccine or NS as placebo. Allocation will be random and double blind. Repeat CHMI will be done with PfSPZ Challenge (NF54) and PfSPZ Challenge (7G8), given in a randomized sequence. All immunizations are given by direct venous inoculation (DVI).