Glossary
Viral Load
Viral load is the amount of virus, most often HIV, present in a person's blood, and keeping HIV's viral load undetectable through treatment means it cannot be sexually transmitted.
Viral load refers to the quantity of a virus, usually HIV, circulating in a person's blood, measured in copies per milliliter. In HIV care it is a central number: a high viral load means the virus is actively replicating, while consistent antiretroviral therapy can lower it to undetectable levels, generally under 200 copies per milliliter. Reaching and maintaining an undetectable viral load keeps the person healthy and, according to the CDC and NIH, means there is effectively no risk of transmitting HIV to sexual partners. This evidence is the basis of the U=U message, short for Undetectable equals Untransmittable. Regular viral load testing is a cornerstone of both HIV treatment and prevention.