The proof-of-concept AMP studies demonstrated that a broadly neutralizing antibody (bnAb) called VRC01 was effective at preventing the acquisition of HIV strains to the 30% of strains that were sensitive to the bnAb. This finding was seen both in Sub-Saharan Africa and the U.S. and South America. VRCO1 did not prevent the acquisition of HIV to strains that were resistant to the bNAb. As the resistant strains constituted nearly 70% of the circulating strains in these regions, there was no difference noted between the VRC01 arms and placebo arm in terms of overall prevention of HIV acquisition. The sensitivity to bNAbs was assessed by a laboratory test that measures a virus’ susceptibility to neutralization by an antibody.