The fact that people infected with HIV who are virally suppressed cannot sexually transmit the virus to others is now accepted in the HIV/AIDS community as a result of accumulating evidence since the early 2000s. In early 2016, the Undetectable=Untransmissable (U=U) slogan was launched by the Prevention Access Campaign to promote the finding. The campaign has been rapidly gathering momentum, having been endorsed by more than 400 organisations from 60 different countries since its launch. Last month, the US Centers for Disease Control and Prevention (CDC) joined the movement by endorsing the science in a letter released on National Gay Men's HIV/AIDS Awareness Day.

The evidence to support the effectiveness of viral suppression in blocking transmission is clear. In addition to some smaller studies done since 2000, three larger studies of sexual HIV transmission in thousands of serodiscordant couples including thousands of acts of sex were done between 2007 and 2016, with, strikingly, not a single case of sexual transmission of HIV from a virally suppressed HIV-positive person to their HIV-negative partner reported. The HPTN 052 trial, the largest study to date, studied 1763 serodiscordant couples (both homosexual and heterosexual) from nine different countries and randomly assigned HIV-positive participants to either early or delayed antiretroviral treatment (ART). Interim results published in 2011 showed that 39 HIV-negative partners had become HIV positive so far, of which 28 were phylogenetically linked (ie, 28 people acquired their infection from their partner). Of these 28, only one occurred in the early ART group.

After this analysis, ART was then offered to all patients with HIV and all patients continued to be followed up to 2015, with the final results published in September last year. Over the entire course of the study, 78 infections were observed, of which phylogenetic linkage was established in 72. Of these infections, 46 were linked to the HIV-positive partner, eight of which occurred after the partner commenced antiretroviral therapy. Of these final eight, four occurred before viral suppression and the other four occurred when ART failed to achieve viral suppression. In other words, not one virally suppressed HIV-positive patient transmitted their infection to their partner during the entire study. Read more via the Lancet