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.

Detailed report of the PARTNER results.

The PARTNER 2 study also reported zero transmissions.

This was after almost 800 gay couples had sex more than 77,000 without condoms.

PARTNER2 results at IAS conference – August 2018.

PARTNER2 results in the Lancet – May 2019.

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 photo1PARTNER 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.

PARTNER photo2Even 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 is for partnerships where the positive partner is on ART and when they do not always use a condom when having sex. The study is also looking 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.

Since then the PARTNER study closed and an extension called PARTNER2 enrolled almost 1000 gay couple to get the same level of evidence for gay men.

Leaflet about PARTNER 2 study (PDF file)

Enrolment criteria (this study is now closed and completed)

To join the PARTNER 2 study you needed to have been a gay couple with the following.

The HIV positive partner

  • Have an HIV negative partner.
  • Are on HIV medication.
  • Have had sex without a condom (vaginal or anal) with your HIV negative partner in the last month before you start in the study.
  • Expect to have sex again with your HIV negative partner.

The HIV negative partner

  • Have an HIV positive partner.
  • Your HIV positive partner is on HIV medication.
  • Have had sex without a condom (vaginal or anal) with your HIV positive partner in the last month before you start in the study.
  • Expect to have sex again with your HIV positive partner.

UK sites

  • Birmingham: Birmingham Heartlands Hospital
  • Brighton: Lawson Unit, Royal Sussex Country Hospital
  • Bristol: Southmead Hospital
  • Cardiff: Cardiff Royal Infirmary
  • Coventry: Coventry and Warwickshire Hospital
  • Edinburgh: Western General Hospital
  • Leicester: Leicester Royal Infirmary
  • Manchester: North Manchester Hospital

London centres

  • Royal Free Hospital
  • St. Stephens Centre/Kobler clinic
  • Royal London Hospital
  • Homerton Hospital
  • North Middlesex Hospital
  • King’s College Hospital
  • St. Thomas Hospital
  • Mortimer Market Centre
  • St. Mary’s Hospital

For more information ask your doctor or HIV clinic, or contact the i-Base phoneline.

PARTNER study website.

CHIP website (full study documents).

Information about viral load and risk of transmission from the i-Base guide to HIV transmission and testing.