What does undetectable = untransmittable (U=U) mean?

'Undetectable = Untransmittable' (U=U) is a campaign explaining how the sexual transmission of HIV can be stopped.

When a person is living with HIV and is on effective treatment, it lowers the level of HIV (the viral load) in the blood. When the levels are extremely low (below 200 copies/ml of blood measured) it is referred to as an undetectable viral load. This is also medically known as virally suppressed. At this stage, HIV cannot be passed on sexually.

This scientific evidence was gathered from several studies. The studies included thousands of heterosexual and gay couples in which one partner had HIV and the other did not. Over the course of the studies, they found that there was not a single HIV transmission from an HIV-positive partner who had an undetectable viral load.

When a person is undetectable, condoms are not required to prevent HIV transmission, but being undetectable does not protect against other sexually transmitted infections.

U=U applies to transmission through sex only. We have more information about the risk of transmission through other routes, including pregnancy and breastfeeding, and sharing needles.

There's much more information about U=U in a more detailed page on this website.

We have provided a U=U page specifically for HIV-negative people. As well as U=U, PrEP is another way to prevent HIV transmission, for HIV-negative people who may not know the HIV status of their sexual partner(s) or whose sexual partner(s) is not undetectable.

You can also read more about the key U=U studies:

• PARTNER 1
• PARTNER 2
• Opposites Attract
• HPTN 052: initial analysis and final analysis.