HIV Treatment as Prevention (TasP)

Table of Contents

What Is "Treatment as Prevention?"

Treatment as prevention (or TasP) refers to ways in which we can use HIV drugs, or HIV treatment, to lower the risk of spreading HIV. For people living with HIV (HIV+), taking HIV drugs can reduce their viral load, thus making their blood, vaginal fluids, breast milk, and semen (cum), much less likely to pass HIV on to others. For people who are HIV-negative, taking HIV drugs can protect against becoming HIV+ if they are exposed to HIV.

Preventing Mother-To-Child Transmission (PMTCT)

Treatment as prevention has been in use since the 1990s, when research showed that pregnant women living with HIV who used Retrovir (an HIV drug also called zidovudine or AZT) greatly reduced the risk of spreading HIV to their babies. It has now become standard practice to test pregnant women for HIV, provide HIV drugs to women living with HIV during pregnancy, delivery, and breastfeeding, and give HIV drugs to the babies of women living with HIV. All of this is referred to as preventing mother-to-child transmission (PMTCT); PMTCT is also known as perinatal or vertical transmission. If a mother takes the correct medical precautions, the chances of spreading or transmitting HIV to her baby can go down from about one in four (when not taking any HIV drugs) to less than one in 100 (when taking proper HIV drugs).

Treatment as Prevention in Sexually Active Adults

In 2011, an important study called HPTN 052 showed that HIV treatment could greatly reduce the chances of an adult living with HIV spreading HIV to another adult through sexual contact. This study took place in Africa, Asia, and the US, and it showed that members of heterosexual couples who were living with HIV and took HIV drugs could reduce the spread of HIV to their HIV-negative partners by up to 96 percent. It is important to note that this effect occurred when the members of the couples living with HIV took HIV drugs even though they did not have any HIV-related symptoms and their CD4 counts were between 350 and 500.

Treatment With a Public Health Twist

Based on the results of the HPTN 052 study, Michel Sidibé, the Executive Director of UNAIDS, stated that:

This breakthrough is a serious game changer and will drive the prevention revolution forward. It makes HIV treatment a new priority prevention option

-- from "Groundbreaking trial results confirm HIV treatment prevents transmission of HIV"

In fact, the HPTN 052 study changed the look of HIV prevention; now an additional tool -- treatment -- had been added to the prevention toolbox. Here's how it works, from a public health (vs. individual health) point of view: if a large enough number of people living with HIV could be treated so that their viral loads dropped to an undetectable level, they would be much less likely to spread HIV, and the number of new infections would drop remarkably. In public health or population terms, this is referred to as a drop in the "community viral load."

"Test and treat" strategies depend on math-based models of how treatment as prevention will change the course of the epidemic. These public health models recommend universal HIV testing to identify people living with HIV, followed by immediate treatment of all people living with HIV, which is now in accordance with all HIV treatment guidelines.

In recent years, studies have shown that how well treatment as prevention works can vary, depending on several factors. These include:

  • Healthcare systems able to provide testing, linkage to care, and HIV drugs
  • Willingness and ability of people to get tested for HIV (HIV-related stigma and discrimination make people less likely to get tested)
  • Willingness and ability of people living with HIV to stick to their HIV drug regimens so that they remain virally suppressed.

Unfortunately, the first major research study of this ‘test and treat' strategy (ANRS 12249) showed that HIV treatment did not reduce new infections in the community. Scientists at the AIDS 2016 conference in South Africa reported that the study was successful in treating more community members, but apparently many people newly diagnosed with HIV did not take HIV drugs, thus making "treatment as prevention" ineffective.

Additional Methods of Treatment as Prevention

While treatment as prevention is often discussed solely in the context of treating people living with HIV, there are also opportunities for treatment to serve as prevention for HIV-negative people.

PrEP (Pre-Exposure Prophylaxis)

PrEP stands for Pre-Exposure Prophylaxis. It means taking medicine before being exposed to something to prevent yourself from getting a disease or condition. When we talk about PrEP in connection to HIV and women, we are referring to the idea of HIV-negative women taking HIV drugs to reduce their risk of getting HIV if they are exposed to it. This can be especially helpful when HIV-negative women whose male partners are living with HIV want to get pregnant. Research has shown that PrEP is a promising tool that women can use to prevent HIV infection without their partners' cooperation. For more information on PrEP, please see our fact sheet on PrEP for Women.

PEP (Post-Exposure Prophylaxis)

PEP stands for Post-Exposure Prophylaxis. It refers to taking HIV drugs for about a month immediately after possible exposure to HIV (e.g., needle-stick, sexual assault, unprotected sex). For PEP to be effective, it must be taken as soon as possible after exposure to HIV -- within the first 72 hours if possible.


Researchers continue to examine the promise of treatment as prevention as a real game-changer in changing the course of the HIV pandemic. A recent study showed that, in serodifferent heterosexual couples, taking PrEP as a "bridge" -- the HIV-negative partner takes PrEP while the partner living with HIV takes the first six months of antiretroviral treatment -- produced a 96 percent reduction in the spread of HIV. Treatment as prevention is important because it can not only positively affect the health and well-being of those living with HIV, but also serve to protect those who are HIV-negative.