‘Undetectable equals untransmittable’ means you can’t sexually transmit HIV while on successful therapy

“U=U” stands for “undetectable equals untransmittable.” It means that people with an undetectable viral load cannot transmit HIV through sex.

Undetectable viral load means bringing the amount of HIV in blood down to such a low level that it can’t be measured on a viral load test. 

HIV therapy should bring viral load down to less than 20 or 50 (copies per milliliter, or mL, of blood plasma). (The lowest amount of HIV that can be measured depends on the viral load test being used.) 

To be untransmittable, your viral load doesn’t actually have to be undetectable. It just needs to be less than 200! This is called “virally suppressed.” And it’s the level found to make HIV untransmittable in research.

U=U has a scientific name: TasP, which stands for treatment as prevention. 

There’s more to U=U/TasP than being virally suppressed. A person must be on the same HIV regimen (stable therapy) and virally suppressed for at least six months, according to the U.S. Department of Health and Human Services (DHHS) HIV treatment guidelines. Other guidelines have other considerations, such as two undetectable viral load test results in a row (at least several weeks apart), according to the New York State Department of Health AIDS Institute (go to hivguidelines.org). Most people achieve undetectable viral load in about two weeks. Maintaining that status is obviously key. 

Medical providers should tell people about U=U, according to the DHHS guidelines. It may help motivate people to maintain their care, but also help overcome the stigma that blocks testing and treating, DHHS writes.

But, says DHHS, providers should remind people that not taking their meds correctly or having a treatment interruption can make transmission possible.  

Viral load can go back up within about two weeks of stopping treatment. There’s a lot of help available around adherence. See bit.ly/NIH-adherence-factsheet.

Remember that an undetectable viral load does not stop anyone from picking up other STIs or from passing those on. Condoms help if you want to prevent STI transmission.

It’s not yet known if undetectable viral load can prevent transmission through needle sharing or the use of other injection equipment. (Although there is some evidence that it does lower the risk.)

And while it definitely lowers transmission to infants, a very small risk of transmission during pregnancy remains and has also occurred during breastfeeding (less than 1%) despite undetectable viral load. 

Some people refer to a third “U”: “universal access” to healthcare.

Credit goes to Bruce Richman and the Prevention Access Campaign for creating the U=U educational and advocacy campaign; go to preventionaccess.org.

There are two major biomedical strategies for ending HIV today: U=U and PrEP. PrEP stands for pre-exposure prophylaxis, which means taking medicine to prevent infection before a possible HIV exposure. There is also PEP, or post-exposure prophylaxis, in which medication is taken for 28 days starting within 72 hours of a potential HIV exposure.

Go to hiv.gov/tasp. Read the section on TasP from DHHS HIV treatment guidelines at clinicalinfo.hiv.gov/en/guidelines/adult-and-adolescent-arv/antiretroviral-therapy-prevent-sexual-transmission-hiv. The TasP section begins on page F-1 of the guidelines.

“The science is clear. People living with HIV can feel confident that if they have an undetectable viral load and take their medications as prescribed, they cannot pass on HIV to sexual partners (Undetectable = Untransmittable, U=U).

“U=U offers freedom and hope. For many people living with HIV and their partners, U=U opens up social, sexual, and reproductive choices they never thought would be possible.”

—Prevention Access Campaign