Participants will be randomized to receive VRC01 mAb by intravenous (IV) infusion at a dose of 10 mg/kg or 30 mg/kg every 8 weeks, or to receive control infusions every 8 weeks. All participants will receive the VRC01 antibody or placebo by IV infusion at Weeks 0 (study entry), 8, 16, 24, 32, 40, 48, 56, 64, and 72. For 3 days following each infusion, participants will be asked to record and report any symptoms to study researchers.