Breakthrough study: HIV treatment prevents transmission of virus between partners

​Results from the PARTNER2 study confirm that effective HIV treatment prevents transmission of virus between gay men. This will improve the quality of life for HIV positive people and their partners globally.

A new study lead by researchers at Rigshospitalet provides scientific evidence that effective HIV treatment prevents transmission of virus between gay men. The PARTNER2 is the largest study to look at the risk of HIV transmission when the positive partner is on effective treatment (ART). 

The researchers have been following almost 1,000 gay male couples from 14 different countries in Europe, where one partner was HIV-infected and on suppressive ART, and the other partner was HIV-negative. The study followed couples from September 2010 to April 2018, over which time couples reported almost 77,000 episodes of condomless anal sex with no linked HIV transmission occurring. 

The results underline the importance of earlier diagnosis and treatment. Professor Jens Lundgren, professor in Infectious Diseases at Rigshospitalet, University of Copenhagen and Co-PI for the PARTNER study, comments:

“In 2015 we proved that it was better to start HIV treatment as soon as possible. We have now provided the scientific evidence for how effectively treatment prevents further sexual transmission”. 

Photo: Professor Jens Lundgren

PARTNER2 was an extension of the earlier PARTNER1 study, which also found zero transmissions in a study population where 65% of couples were heterosexual. Some gay couples in PARTNER2 were also included in the PARTNER 1 results. The new results provide a similar level of confidence that HIV transmission risk in gay men through condomless sex is effectively zero as PARTNER1 provided for heterosexual couples. 

No linked HIV transmissions 

Some of the originally HIV negative men did becomes positive during the study, but by comparing the structure of each virus it was possibile to show that the two infections were different, and to conclude that the new infection was not acquired from the HIV positive partner. This uses a technique called phylogenetic analysis. In the PARTNER2 study, a total of 15 HIV-negative gay men became HIV positive during follow up. 

Researchers from the University of Liverpool led by Professor Anna Maria Geretti, undertook the phylogenetic analyses. Professor Geretti comments: 

“Each individual HIV infection has its own genetic characteristics. Comparing the genomes of different viruses can show how similar or indeed dissimilar one virus is to another. In PARTNER2, the phylogenetic analysis showed that in all cases of new HIV infections occurring during the study, the virus was so different that it must have come from someone other than the HIV-positive partner on suppressive ART.”

Simon Collins, an HIV positive treatment activist at HIV i-Base, London, and one of the community representatives involved in the study said: “PARTNER2 has met the community demand from gay men to have accurate data about our health. There is no evidence that HIV transmission can actually occur when viral load is undetectable. Our data continue to support the international U=U awareness campaign." 

The study is supported by a grant from the Danish National Research Foundation.

For further information about the Partner study see CHIP's homepage.


Jens Lundgren, MD DMSc 

Professor, Director of CHIP

Academic chair, dep of infectious diseases

Direct: + 45 35 45 57 51

Cell: + 45 40 87 93 03


PA: +45 35 45 57 63 (Lisbeth Jørgensen)

Rigshospitalet, University of Copenhagen

Department of Infectious Diseases, Section 8632

Centre for Cancer and Organ Diseases

Esther Møllers Vej 6

DK-2100 Copenhagen Ø, Denmark

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