"Undetectable" means that a test cannot detect the virus in the blood of a person living with HIV, although extremely small amounts of HIV are still present. Someone who takes HIV treatment and is "undetectable" for 6 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 will return to a detectable level, which then increases the risk of transmission.
Undetectable. U=U, short for "undetectable = untransmittable". Treatment as prevention, or "TasP". Basically, these terms all mean the same thing: If a person living with HIV stays undetectable for 6 months or more while on treatment, they cannot transmit HIV through sex.
Three global studies showed no HIV transmissions within mixed-status couples when the partner with HIV was undetectable for 6 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.
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For more information on the U=U campaign and the science behind U=U, visit Prevention Access Campaign.
Visit our U=U for advocates page for more in-depth resources and information.