PARTNER and PARTNER 2 studies
This page is part of Pocket ART, an easy guide to HIV treatment.
The PARTNER study reported zero HIV transmissions from a positive partner on ART to their negative partner.
This was after couples in the study had sex more than 58,500 times without using condoms.
The PARTNER 2 study also reported zero transmissions.
This was after almost 800 gay couples had sex more than 77,000 without condoms.
Together, these studies contributed to the evidence that support U=U. This means there is zero risk of transmitting HIV when viral load in undetectable.
PARTNER 2 continued PARTNER but only in gay men.
PARTNER 2 included many UK sites. The study quantified the risk of HIV transmission in serodifferent couples where the HIV positive partner is using HIV treatment.
Even though we know generally which are high and low risks, very few studies have quantified this. Very few studies provide data on the risk from anal sex – whether gay or straight. This is still the case even after 25 years of research. There is very little data on the risks of sexual transmission in gay men.
Even though the orignial PARTNER study was open to all serodifferent couples, the PARTNER 2 study in now focused only on gay men.
Condoms are a safe and effective way to protect against transmission. But condoms can break or slip off and that not everyone uses a condom every time.
PARTNER 2 was for partnerships where the positive partner is on ART and when they do not always use a condom when having sex. The study also looked at why condoms are not always used.
The original PARTNER study enrolled both straight and gay couples. The first results were presented in 2014. Theses results were published in 2016.
The extension called PARTNER2 enrolled almost 1000 gay couples to get the same level of evidence for gay men.
Leaflet about PARTNER 2 study (PDF file)
This study is now closed and completed.