For the competition ELISA, a fixed amount of total IgG from a U.S. vaccinee (designated as US-total IgG), which gives approximately an O.D. value of 3 (approximately 30-40 mg/ml of total IgG in ELISA well), was mixed with 2-fold dilutions of non-AMA1(3D7) IgGs from Malian children (ranging from 2 to 133 mg/ml in ELISA well). The mixtures were tested by ELISA using an AMA1(3D7) or AMA1(FVO)-coated plate using the standard ELISA procedure, and the direct O.D. value was used as a final readout, instead of ELISA units.