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HIV Viral Load and Transmission FAQ

October 11, 2016

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Table of Contents

Can a Person With HIV Who Has An Undetectable Viral Load Transmit HIV?

No. A person living with HIV on antiretroviral therapy (ART) with an undetectable HIV viral load in their blood for at least six months has a negligible risk of transmitting HIV to a sexual partner. Negligible means: so small as to not be worth considering; insignificant. Therefore, when describing the risk of HIV transmission HIV experts have said: "not infectious", "virtually zero risk" and "cannot transmit the virus."1

Related: HIV Undetectable Does Equal Uninfectious: The Swiss Statement and the Vindication of Pietro Vernazza


What Is an Undetectable Viral Load?

Viral load refers to the amount of HIV in a blood sample of a person living with HIV. Generally, the higher the viral load, the more likely you are to transmit HIV. ART can reduce a person's viral load to the point where it is so low (usually under 40 copies/ml depending on the test) that it cannot be detected by measurements.2 This is called "having an 'undetectable viral load,'" which prevents the sexual transmission of HIV while simultaneously improving the health of a person living with HIV.1 It does not fully clear the virus from the body or cure someone of HIV.

What Is the Evidence?

The conclusion is based on the force of real world and research experience including PARTNER, HPTN 052, Opposites Attract and the Swiss Statement.3-11 For instance, in the most recent study called PARTNER, there were ZERO transmissions out of 58,000 condomless sex acts between people with HIV with undetectable viral loads and their partners who are HIV negative. As of this writing, there have been no confirmed reports of anyone transmitting HIV with an undetectable viral load in these studies.11

Is the Risk Zero?

In real world terms, yes the risk is zero. In theoretical terms, the risk is a tiny fraction close to zero. The challenge is that scientific studies can never prove that risk is absolute zero. Through statistical analysis that number will keep getting closer and closer to zero. Researchers agree that because the actual HIV transmission risk is either zero or extremely close to zero, a person with HIV with an undetectable viral load is considered "not infectious" to their sexual partners.1

Related: Sex 58,000 Times With Undetectable Partners = Zero HIV Transmission: Learn More

Why Are Some Groups Saying an Undetectable Viral Load Reduces Risk by 93-96%?

It's a widespread mistake when reporting the HPTN 052 study's findings. This study looked at the transmission risk from the first day a person with HIV starts treatment. The reason there was a 96% risk reduction (based on the study's interim results) or a 93% risk reduction (based on the study's final results) is because there were HIV transmissions before ART had the chance to suppress the virus. If only transmissions after the first six months of ART are considered, the risk reduction would have been 100% with a transmission risk of zero.3,11-14

What Does "Treatment as Prevention" Mean?

Treatment as prevention (TasP) refers to any HIV prevention method that uses ART to decrease the risk of HIV transmission to a sexual or needle sharing partner, or from mother to baby. ART reduces the HIV viral load in the blood, semen, vaginal fluid and rectal fluid to very low levels, and as a result reduces HIV transmission.15 When the virus in the blood is reduced to undetectable levels, the risk of sexual transmission of HIV is negligible.

Does Everyone Who Starts HIV Treatment Become and Remain Undetectable?

Nearly everyone who starts ART finds a drug regime that works within six months.16 About one out of six people will will need additional time to find the right treatment due to tolerance and adherence issues. People who remain undetectable for a year or more with excellent adherence to treatment, are highly unlikely to experience a viral rebound, known as "treatment or virological failure".17 Treatment failure after sustained viral suppression is rare and almost always related to poor treatment adherence.18

Do Viral "Blips" Increase the Chance of Transmission?

Viral blips have not been shown to increase the transmission of HIV.1,7 Small transient increases in viral load (between 50 and 1000 copies) known as "blips"19 sometimes result on effective ART when people are adherent, but typically return to undetectable levels without any change in treatment. Unless the viral blips start to increase in frequency, they do not mean treatment isn't working and are normally not of concern to providers.1,7

Does Having an STI Affect the Chance of HIV Transmission?

Having an STI is not significant to HIV transmission when the partner with HIV has an undetectable viral load.7,9 An STI in the presence of a detectable viral load may increase the risk of HIV transmission.

Why Do Some People Have Detectable Viral Loads?

Some people may choose not to be treated or may not be ready to start treatment. Access to adequate and stable healthcare is a serious barrier to treatment in many parts of the world. Others start treatment but have challenges with adherence for a variety of reasons such as stigma, mental health and substance abuse, unstable housing, difficulty paying for medications, drug resistance and/or intolerable side effects.20

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This article was provided by Prevention Access Campaign.

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