Updated: Mar 29, 2020
Undetectable = Untransmittable (U=U) is a global campaign involving 850 organisations across 97 countries that teaches the importance of Antiretroviral treatment (ART) in preventing the spread of HIV.
This campaign also highlights the fact that with proper treatment, People Living with HIV (PLHIV) whose partners are HIV negative don't have to worry about transmitting their infection to their partners.
Research carried out over the past twenty years, involving both heterosexual and homosexual couples and for all types of sex, indicate that when someone has shown continuous undetectable levels of HIV (for 6 months) it is impossible for them to transmit the virus.
HIV Transmission (to others) depends on the viral load. A high viral load makes transmission very easy, which is why HIV is most easily transmitted to partners in the acute infection stage when the viral load is very high. When antiretroviral therapy is taken everyday, the viral load can be reduced to the point that there isn't enough virus in the blood to be detected in a lab, or to be transmitted to this others. This is known as viral suppression .
This only works if medication is taken regularly, and your viral load has been shown to be consistently suppressed, which is why you'll need to have consecutive Viral Load tests over 6 months which show an undetectable result before you can be 100% confident in the U=U strategy of prevention.
If you happen to miss a dose of medication, or you have a viral load blip (below 200 copies/mL), U=U can still work. Research indicates that either of these events will not affect your ability to transmit the HIV virus to your partner. However, if you miss more than one dose in a 3 month period, it would be important to use other prevention strategies until you are able to retake a viral load test and take your medication consistently.
It's also important that the U=U strategy only applies to sexual exposures to HIV. Even when undetectable, there is still a minor risk of transmitting HIV through pregnancy, delivery, breastfeeding and needle sharing.
If you'd like to find out more about U=U, here are some resources from various health organisations which may help. :
American Center for Disease Control & Prevention (CDC)