Medicines to treat HIV can eliminate the risk of sexual transmission. In August 2016, the New York City (NYC) Health Department agreed with other public health and medical organizations that people with HIV who maintain an undetectable viral load for at least six months do not transmit HIV through sex. In September 2017, the Centers for Disease Control and Prevention and the New York State Department of Health (PDF) agreed with this finding, which is known as "Undetectable = Untransmittable," or "U = U".
How Does HIV Treatment Prevent HIV Transmission?
Antiretroviral medicines are very effective at controlling HIV. They do not cure HIV infection or remove the virus from the body, but if taken every day, as prescribed, HIV medicines stop the virus from multiplying. This prevents the virus from damaging the immune system and stops sexual transmission to others.
What Does "Undetectable" Mean?
"Undetectable" means that the level of HIV in a person's blood is so low that it doesn't show up on a viral load test. If a person is undetectable, HIV can still be hiding in their body, but the amount is so low that HIV cannot be passed to others through sex.
How Do We Know That "Undetectable = Untransmittable"?
Three recent studies -- HPTN 052, PARTNER and Opposites Attract -- followed male couples and heterosexual couples in which one partner was HIV-positive and the other HIV-negative. During these studies, not one HIV-positive person who was taking antiretroviral medicines and was virally suppressed passed HIV to their negative partner. In the PARTNER and Opposites Attract studies, male couples had anal sex without condoms more than 34,000 times and heterosexual couples had vaginal or anal sex without condoms more than 36,000 times without a virally suppressed partner ever passing HIV to the negative partner. This is strong evidence that people do not sexually transmit HIV if they have an undetectable viral load.