In parallel to CHMI with PfSPZ Challenge (NF54) during the optimization phase, a total of nine volunteers will receive either 800, 1,600 or 3,200 PfSPZ Challenge (7G8) (PfSPZ Challenge (7G8) dose finding) to assess safety, tolerability and infectivity of PfSPZ Challenge (7G8) in malaria-naïve healthy adult volunteers.