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What Does “Undetectable = Untransmittable” Mean?

“Undetectable” means that a lab test cannot detect the virus in the blood of a person living with HIV. Although extremely small amounts of HIV are still present, these are not considered infectious. Someone who takes HIV treatment and is “undetectable” for six or more continuous months does not transmit the virus through sex.

Undetectable also means the virus is being well controlled by HIV meds. If a person with undetectable HIV stops their medications, the virus returns to a detectable level, which then increases the risk of transmission.

The lingo

U=U is short for “undetectable = untransmittable.” Treatment as prevention, or “TasP.” Generally, these terms mean the same thing: If a person living with HIV stays undetectable for six months or more while on treatment, they cannot transmit HIV through sex.

The scientific evidence

Three global studies showed no HIV transmissions within mixed-status couples when the partner with HIV was undetectable for six or more months. This included more than 126,000 acts of reported condomless sex among mixed-status heterosexual and gay male couples. (The studies were HPTN 052, PARTNER, and Opposites Attract.) To date worldwide, there are no verified reports of someone getting HIV from a partner who is undetectable.

Related Resources

Prevention Access Campaign

Prevention Access Campaign (PAC) is a global non-profit organization dedicated to saving lives and ending the HIV epidemic by making Undetectable = Untransmittable (U=U) a reality for all people living with HIV. 

NYC Health: Undetectable Equals Untransmittable (U=U)

This page from the New York City Department of Health provides information on HIV, its treatment, and testing services.

Live Undetectable

"The Undetectables" provides a network of support and resources to help you get what you need. Take this powerful step for your own health and the health of your community.

HIV Treatment, the Viral Reservoir, and HIV DNA

This page from the National Institutes of Health describes antiretroviral therapy (ART) and its role in treating and preventing HIV infection.