Spotlight Center on HIV Prevention Today


Negligible Risk: Updated Results From Two Studies Continue to Show That Antiretroviral Treatment and an Undetectable Viral Load Is a Highly Effective HIV Prevention Strategy

September 6, 2016

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What This Means

The results of both HPTN 052 and PARTNER reaffirmed that ART is a highly effective strategy to prevent the sexual transmission of HIV. Both studies found that no HIV transmissions occurred when the partner on ART was undetectable. In HPTN 052, only eight transmissions occurred when the HIV-positive partner was on treatment, and the viral load was likely not undetectable. Importantly, all couples in both studies were engaged in regular care, such as ongoing viral load monitoring, testing for sexually transmitted infection (STI), and adherence and risk-reduction counselling. These supports likely helped improve the HIV prevention benefit of ART.

The findings from these studies provide insight into the rare circumstances where HIV transmission can occur within the context of a serodiscordant relationship in which the positive partner is on ART. These include the period between starting ART and achieving an undetectable viral load and virological failure.

From these two studies we know that sex with partners outside of the main relationship accounted for a substantial number of HIV transmissions to the HIV-negative partner. In HPTN 052, 33% of all HIV transmissions occurred from outside the main relationship. In PARTNER, 100% of all HIV transmissions occurred from outside the main relationship.


Consensus on the Risk of Sexual Transmission of HIV When the Viral Load Is Undetectable

Based on the cumulative evidence to date, community members and leading researchers have endorsed the following Prevention Access Campaign statement:

"People living with HIV on ART with an undetectable viral load in their blood have a negligible risk of sexual transmission of HIV. Depending on the drugs employed it may take as long as six months for the viral load to become undetectable. Continued and reliable HIV suppression requires selection of appropriate agents and excellent adherence to treatment. HIV viral suppression should be monitored to assure both personal health and public health benefits."

Spread the Word

It is important that community members -- both people living with HIV and those at risk for HIV -- be given information and offered counselling about ART and undetectable viral load as a highly effective strategy to prevent the sexual transmission of HIV. The following key messages are important:

  • ART is a highly effective HIV prevention strategy (when the viral load is undetectable) regardless of whether condoms are used. However, using condoms as part of a combination HIV prevention strategy can reduce the risk for other STIs, particularly if couples are having sex outside the relationship.
  • It is possible for viral load to increase if ART stops working due to poor adherence to medications or drug resistance. Regular adherence to medications and viral load testing is important to ensure that ART is working and an undetectable viral load is maintained.
  • It can take up to six months for the viral load to reach undetectable levels once treatment has started and some people may find it more difficult to reach undetectable levels. Guidelines generally recommend that the viral load be undetectable for at least six months (as determined by two consecutive viral load tests) prior to using ART as a prevention strategy.
  • In a non-monogamous relationship in which the HIV-positive partner is on successful ART, the main risk of HIV transmission comes from outside the relationship. Couples should be encouraged and supported to discuss their relationship status with each other (for example, monogamous or non-monogamous) and consider using HIV prevention strategies, such as pre-exposure prophylaxis or condoms, with outside sex partners if the relationship is non-monogamous.


  1. Cohen MS, Chen YQ, McCauley M, et al. Antiretroviral therapy for the prevention of HIV-1 transmission. New England Journal of Medicine. 2016;375:830-9. Available from:
  2. Rodger AJ, Cambiano V, Bruun T, et al. Sexual activity without condoms and risk of HIV transmission in serodifferent couples when the HIV-positive partner is using suppressive antiretroviral therapy. Journal of the American Medical Association. 2016;316(2):171-81. Available from:
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If We Act to Remove Structural, Behavioral and Social Barriers, We Can End the HIV Epidemic With the Medicines We Already Have

This article was provided by Canadian AIDS Treatment Information Exchange. It is a part of the publication CATIE News. Visit CATIE's Web site to find out more about their activities, publications and services.

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