Development of fraction of X4 viruses. Development of predicted fraction of X4-using viruses during Vicriviroc treatment for four patients (right vertical axes, orange squares), and the contribution of that fraction to the absolute viral load (left vertical axes, black circles). Labels "R5" (R5-using) and "DM"(dual/mixed or X4-using) are Trofile® results at the given times. The dotted line marks the 10% detection rate of standard Trofile® assay. Naming was adopted from .