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Treatment Is Prevention, Part 1

“Treating HIV is among the most effective ways to prevent transmission.” 1

It is now accepted science that if a person living with HIV has an undetectable viral load, they will not transmit the virus to their sexual partners. This life-changing concept is referred to as U=U, Undetectable = Untransmittable, or TasP: Treatment as Prevention. This information is supported by major health groups from the CDC to WHO, yet many people have not heard it yet.2,3

U=U? TasP?

The Prevention Access Campaign, a group of people living with HIV, created the concept of U=U, Undetectable = Untransmittable. They saw the studies showing that an undetectable viral load prevents sexual transmission of HIV, and they wanted to spread the word. 

TasP describes the same concept. When a person living with HIV takes antiretroviral therapy (ART) and reaches a low viral load, they are not only supporting their own health but the preventing the transmission of HIV. TasP is the concept. U=U is the message.4

What does the science think about the effectiveness of treatment as prevention?

It’s a big thing to be told you can trust your treatment, or your partners’ treatment, to reduce the risk of acquiring HIV. What makes the scientists confident about this? Many studies now support the idea.

  • The first study to prove this was published back in 2011. Researchers monitored 1,763 mixed-status male-female couples (1 partner positive, the other negative) who were having sex without a condom. They found starting ART at the time of diagnosis decreased the chance that the negative partner would test positive. ART also kept the positive partner healthier. They then followed these couples for 5 years, and found no transmission when the viral load was suppressed.5,6
  • The 2014 PARTNER1 study: Another 1,166 mixed-status couples were followed for an average of over a year. These couples also had no transmission if the viral load was suppressed (less than 200 copies/ml). About two-thirds were male-female couples, but this time about a third of the couples were gay men.7
  • PARTNER2, published in 2019, focused entirely on 782 gay couples. These couples were followed for an average of 2 years. They had over 76,000 episodes of anal sex without a condom. Again, there was no transmission within the couple when the viral load was suppressed. There were 15 new HIV infections, but by looking at the genetics of the HIV, researchers could see that these were not the same strains of HIV as the 1 carried by the positive partner. This means the virus came from a partner outside the couple.8
  • The 2018 Opposites Attract study 2018 monitored 343 gay male couples for 12,447 events of anal intercourse without a condom. They again found no HIV transmission within the couple if the viral load was under 200.9

In summary: looking at all of these couples together, there were no sexual transmissions of HIV when the viral load was suppressed. None.

Benefits of treatment as prevention

We know that HAART(Highly active antiretroviral therapy) helps people living with HIV to stay healthier. An international study found people who are aware of the TasP message see some other benefits as well.10-13

  • They were more likely to take medicine as prescribed. "I’m actually motivated now to take my medications and adhere to them because I don’t want to be anything other than undetectable because my partner is HIV negative. I’d like to keep it that way."
  • They are more likely to have a suppressed viral load.
  • They describe themselves as having "optimal sexual health."
  • They are more likely to share their HIV status, not just with partners, but with friends and family as well.
  • For some, knowing about TasP may improve their self-esteem or confidence around HIV. A survey of people living with HIV in the United Kingdom found 79 percent said knowing about U=U had a positive impact on how they felt about their HIV diagnosis. As one man said: "It takes the emphasis off the illness and puts it on my health."
  • And in a big picture view, more people with suppressed the viral load means less HIV virus in a community. Less virus in the community means less ability to trasmit.

A new definition for "protected sex"

TasP gives new meaning to the term "protected sex." It tells us that condoms are not the only form of “protection” against HIV transmission. Medications work, too. How well? Four studies with more than 4,000 couples found no transmissions, in either male-female or male-male couples.13-15

As a comparison, condoms are around 90-95 percent effective at preventing HIV transmission. PrEP lowers the risk by about 99 percent. So when ART is taken consistently and the viral load stays low, it’s at least as effective as those options.13-15

These studies give you important information you can use to make confident decisions about your health. But so many people don’t know about it yet. Why the delay, and what questions still need to be answered? Keep reading for more on this topic in part 2.


Dr. Audrey Sheridan is a board-certified obstetrician-gynecologist (OB-GYN) and also a caretaker for her dad. Dr. Sheridan is inspired by people finding their way through life-changing medical situations with resilience and is interested in how we can increase our mental durability in the face of the unpredictable.

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