No, they cannot. A person who is on effective HIV treatment and whose viral load is undetectable cannot transmit HIV to their sexual partners. This groundbreaking development in HIV prevention publicized with the slogan U=U, which stands for undetectable equals untransmittable.

Someone in a relationship with a person living with HIV who has an undetectable viral load may still choose to use PrEP to reduce their or their partner’s anxiety about the idea of HIV transmission, even though there is no actual chance of transmission, or to give the HIV-negative partner a sense of control over HIV prevention in the relationship.