 A maximum of 30 volunteers will be randomly divided into four groups. All volunteers will receive standard weekly chloroquine chemoprophylaxis for a period of 14 weeks 98 days. During this period, groups 1 and 3 will receive six ID injections of PfSPZ Challenge, containing a total of 75,000 PfSPZ of the Pf NF54 strain, on days 8, 36 and 64 immunizations 1, 2 and 3. The control groups 2 and 4 will receive ID injections with normal saline NS on the same days. 