Effective treatment for HIV with antiretroviral drugs reduces the amount of virus in the blood to undetectable levels. NIAID-supported research has demonstrated that people living with HIV who take antiretroviral medications daily as prescribed and who achieve and maintain a durably undetectable viral load have effectively no risk of sexually transmitting the virus to an HIV-negative partner. Read more about how a durably undetectable viral load can prevent HIV transmission with NIAID's fact sheet 10 Things to Know About HIV Suppression.
The NIAID-supported HPTN 052 clinical trial, which involved more than 1,600 heterosexual couples over 10 years, found that starting and sustaining treatment for HIV infection early, when the immune system is relatively healthy, essentially eliminated the transmission of HIV. No HIV transmission was observed when antiretroviral therapy consistently, durably suppressed the virus in the partner living with HIV. While some transmission events did occur in the study, new infections resulted when the partner living with HIV was not fully virally suppressed due to either having just started antiretroviral therapy, or for whom treatment no longer was working and the virus was replicating. The primary finding from HPTN 052 was a 96 percent reduction in risk of infection, which the journal Science hailed as the scientific breakthrough of the year in 2011. Thus, treatment for HIV is a powerful arrow in the quiver of HIV prevention tools.
The HPTN 052 results, along with those of another NIAID-funded trial (the START study), helped influence the World Health Organization in 2015 to recommend that everyone living with HIV should begin treatment upon diagnosis.