 Primary HIV Infection PHI is a unique period when HIV proviral reservoir is smaller than in chronic disease, is likely to be more homogeneous than in later stage disease and hence is more susceptible to immunological elimination. This provides an opportunity to use a vaccine to re-direct HIV-specific immune responses towards genetically fragile regions in the viral proteome. Immunisation in PHI should result in potent immune responses because ART initiated in PHI preserves CD4 function and early ART-mediated viral suppression limits viral diversification, reducing the chance of immune escape. The other key reason for conducting this trial in patients treated in PHI is that, in some patients, an early sustained course of ART started very early in infection may induce a state of viral remission in which therapy can be stopped without any rebound viraemia. This has been most notably reported in the VISCONTI cohort in which post-treatment control was identified in 15.6 of selected individuals. 