The interim results of a study into sero-discordant relationships has shown zero HIV transmissions between men in such couples.
The Kirby Institute’s Opposites Attract study looked at couples where one man was HIV-positive, on treatment and with an undetectable viral load, and the other HIV-negative.
By December 2014, the Kirby Institute in Australia had enrolled 234 gay male serodiscordant couples: 135 of these were from Australia, 52 were from Bangkok, Thailand, and 47 were from Rio de Janeiro, Brazil.
Echoing other similar results, the Opposites Attract study saw no HIV transmissions in its interim results, halfway through.
The chief researcher on the project, Professor Andrew Grulich, said he thought the results were promising.
“These are very exciting results that seem to mirror findings from other important international studies of heterosexual couples, which have provided strong evidence that treatment as prevention works,” said Grulich.
“Essentially, what we are seeing among the gay couples enrolled in Opposites Attract is that HIV transmission is quite unlikely when someone’s viral load is undetectable. In fact, no HIV-negative man in the study has contracted HIV from his positive partner.”
As well as looking at HIV transmissions between such couples, the study also looked at positioning and sexual behaviour in the transmission of HIV.
Grulich said there was a need for a larger sample size.
“The true risk of transmission could be anywhere between zero and 4.2% per year, with a very small chance that the per-year risk could be higher than 4.2%,” said Grulich.
“We still need more gay couples to enrol in Opposites Attract, and we need to continue following up with the couples in the study before we can produce a more conclusive result to fully answer the question of how much HIV treatment reduces HIV transmission between partners in gay, sero-discordant couples.”