8 years, 14 countries, 1,566 people and 77000 episodes of condomless sex later – we can say that undetectable does equal untransmittable for gay men.

Today, Tuesday 24th July, the results of the PARTNER2 study were revealed at the AIDS2018 conference in Amsterdam.

The original PARTNER study shared its initial findings back in 2014. The study followed 888 sero-different (where one partner was HIV positive, on treatment, and undetectable – and the other partner was HIV negative) couples who engaged in condomless sex over six years. There were zero linked partner-to-partner transmissions. The study was criticised, however, for not including enough men who have sex with men.

PARTNER2, an extension of the original trial, was conceived to address these concerns and fill the data gap.

PARTNER2 followed 783 sero-different (where one partner was HIV positive, on treatment, and undetectable – and the other partner was HIV negative) gay couples from 14 countries. Over the eight years the couples clocked up over 77,000 episodes of condomless anal sex. Once again there were zero linked partner-to-partner infections.

There were 15 new HIV infections within the couples followed, but these were analysed and found to have come from partners outside the main relationship. Many of the couples who participated were in open-relationships.

Combining the results from the original PARTNER study and the new PARTNER2 study we have an incredible amount of evidence which allows us to say that Treatment As Prevention (TASP), or Undetectable = Untransmittable (U=U), is just as effective in gay, bi and other men who have sex with men as it is in heterosexual couples.

The results presented by Alison Rodger confirm what many of us knew to be true, but required more evidence to convince the remaining naysayers.

Editor’s note: For the purpose of the PARTNER & PARTNER2 studies the investigators considered ‘undetectable’ to be a viral load below 200 copies/mL – which is several times higher than what we consider ‘undetectable’ in the United Kingdom. 

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