HIV Treatment as Prevention

Purpose

HIV treatment has improved the health, quality of life, and life expectancy of people with HIV. HIV treatment has also had a profound impact in preventing the transmission of HIV to others, known as "Treatment as Prevention" (TasP). This page explores the evidence and CDC's efforts to increase awareness of this prevention strategy.

Image of a person holding a handful of mediation (pills) with a glass of water in the other hand.

Overview

People with HIV should take medicine to treat HIV (antiretroviral therapy, or ART) as soon as possible after diagnosis. Delaying treatment can increase the chances of transmitting HIV to others, getting sick, or developing AIDS.

If taken as prescribed, HIV medicine reduces the amount of HIV in the body (viral load) to a very low level, which keeps the immune system working and prevents illness. This is called viral suppression—defined as having less than 200 copies of HIV per milliliter of blood.

ART can reduce the viral load so much that a test can't detect it (undetectable viral load). Getting and keeping an undetectable viral load is the best thing people with HIV can do to stay healthy. Reducing the amount of virus in the body prevents transmission to others through sex or syringe sharing, and from pregnant person to child during pregnancy, birth, and breast/chestfeeding. This is sometimes called treatment as prevention.12345678910 There is strong evidence about treatment as prevention for some of the ways HIV can be transmitted, but more research is needed for other ways.

Risk of HIV transmission with undetectable viral load by transmission category

Transmission category
Risk for people who keep an undetectable viral load
Sex (oral, anal, or vaginal)
Studies have shown no risk of transmission
Pregnancy, labor, and delivery
1% or less*
Sharing syringes or other drug injection equipment
Unknown, but likely reduced risk
Breast/chestfeeding
Less than 1%, but not zero†

*The risk of transmitting HIV to the baby can be 1% or less if the pregnant person takes HIV medicine as prescribed throughout pregnancy and delivery and gives HIV medicine to their baby for 2-6 weeks after birth.

†If a pregnant person has an undetectable viral load during pregnancy and wishes to breast/chestfeed, they can discuss this with their provider and make a plan together on the best way to breast/chestfeed safely.

The evidence of TasP for sexual transmission

In 2011, the interim results of the HPTN052 clinical trial1 showed a 96% reduction in HIV transmission risk among heterosexual mixed-status (HIV-discordant) couples where the partner with HIV started ART immediately versus those delaying ART initiation. The final results published in 2016 reported that there had been no HIV transmissions within these couples when the partner with HIV had a suppressed viral load.7Genetically linked HIV infections were observed between sexual partners in 8 couples. However, all these transmissions occurred while the partner with HIV was not virally suppressed. Linked HIV transmissions occurred only when:

  • The partner with HIV had started ART but before the partner with HIV had achieved and maintained viral suppression, or
  • The partner with HIV had achieved viral suppression but the ART regimen later failed or the partner with HIV had stopped taking their medication.

Three additional studies—PARTNER, Opposites Attract, and PARTNER2—reported similar results. None of these studies observed any genetically linked infections while the partner with HIV was virally suppressed and the couples were having sex without a condom and not using pre-exposure prophylaxis (PrEP).8910

Most participants with HIV in the PARTNER study had less than 50 copies of HIV RNA per milliliter of blood.8The studies included participants from various countries with over 500 HIV-discordant heterosexual couples, with about half having a male partner with HIV (PARTNER), and more than 1,100 HIV-discordant MSM couples (PARTNER2; Opposites Attract). Combined, these couples engaged in over 125,000 sex acts without a condom or PrEP over more than 2,600 couple-years of observation.

The studies reported transmission risk estimates and their corresponding 95% confidence intervals as:

  • PARTNER study:8

– For any sex among heterosexual and male-male couples: 0.00 (0.00 – 0.30) per 100 couple-years

– For anal sex among male-male couples: 0.00 (0.00 – 0.89) per 100 couple-years

  • Opposites Attract study:9

– For anal sex among male-male couples: 0.00 (0.00 – 1.59) per 100 couple-years

  • PARTNER2 study (which includes data from PARTNER):10

– For anal sex among male-male couples: 0.00 (0.00 – 0.24) per 100 couple-years

Data from the PARTNER2 and Opposites Attract studies produce a combined transmission risk estimate for anal sex without a condom or PrEP among MSM couples of 0.00 (0.00 – 0.21) per 100 couple-years. Pooling data from all three studies produces a combined transmission risk estimate for sex without a condom among heterosexual or MSM couples of 0.00 (0.00 – 0.14) per 100 couple-years. These data provide conclusive evidence of the power of viral suppression in preventing HIV transmission. Although a non-zero risk estimate can never be completely ruled out in a mathematical sense, the data tell us that the best estimate for transmission risk is zero and that future HIV transmissions are not expected when people with HIV remain virally suppressed.

Maximizing the effectiveness of TasP in practice

The success of the TasP strategy depends on achieving and maintaining an undetectable viral load. While many people with HIV taking ART are virally suppressed, some are currently not virally suppressed or do not maintain viral suppression over time.

CDC’s national surveillance data estimate that 65% of all people with diagnosed HIV in 48 states and the District of Columbia in 2022 were virally suppressed.11 Among people in HIV clinical care (defined as either receiving HIV medical care or having a CD4 or viral load test within the past year), about 76% were virally suppressed at their last test.11

In a cross-sectional analysis of people with diagnosed HIV, most were in care in the last 12 months (95%). About two-thirds (63%) achieved and maintained viral suppression over 12 months.12

To help people with HIV and their partners benefit the most from this prevention strategy, it is important to give providers, people with HIV, and their partners clear information regarding the benefits and challenges of achieving and maintaining viral suppression. Challenges include:

  • Time to viral suppression: Most people will achieve an undetectable viral load within 6 months of starting ART. Many will become undetectable very quickly, but it could take more time for a small portion of people just starting ART.
  • Adherence to treatment: Taking HIV medicine as soon as possible after diagnosis and as prescribed is the best way to stay healthy and achieve and maintain an undetectable viral load. Without treatment or with poor adherence, the viral load stays elevated and increases a person’s chance for transmitting HIV. People who are having trouble taking their HIV medicine as prescribed can work with health care providers to improve their adherence. If an individual is experiencing adherence challenges, other prevention strategies could provide additional protection until the individual’s viral load is confirmed to be undetectable.
  • Knowledge of viral load: Regular viral load testing is critical to confirm that a person has achieved and is maintaining an undetectable viral load. Data suggest that people may not know or be able to accurately report their viral load level.13
  • Stopping HIV medication: If a person stops taking their HIV medicine, their viral load will return to around the same level it was before starting their HIV medicine. People who have stopped taking their HIV medicine should talk to their health care provider about their health and use other strategies to prevent sexual HIV transmission.
  • Protection against other STIs: Taking HIV medicine and achieving and maintaining an undetectable viral load does not protect from other sexually transmitted infections (STIs). Other prevention strategies, such as condoms, are needed to provide protection from STIs.
  • Lack of knowledge or awareness about the benefits of viral suppression: Knowledge of the prevention benefits of viral suppression may motivate people with HIV and their partners to adopt.14 Studies show that many people do not know or do not believe that viral suppression works for prevention.

Knowledge about TaSP appears to be increasing over time. However, more work is needed to increase knowledge and awareness among people with HIV and their sexual partners, people without HIV, and those who don’t know their HIV status.15

What CDC is doing

CDC is working with prevention partners to prioritize efforts to maximize the impact of TasP. We will continue strengthening longstanding programs and supporting new efforts through Ending the HIV Epidemic in the U.S..16 Programmatic efforts help expand HIV testing services to people not recently tested or not aware of their HIV status, diagnose people with HIV earlier, link or re-engage them to effective HIV care and treatment, and support adherence to HIV treatment to achieve viral suppression and ultimately reduce transmission.17

Through education campaigns and risk reduction tools and resources, CDC is increasing awareness of prevention strategies and their effectiveness.1819

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Content Source:
HIV; National Center for HIV, Viral Hepatitis, STD, and Tuberculosis Prevention
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