U=U for Advocates

In September of 2017, the CDC affirmed that "People who take ART daily as prescribed and achieve and maintain an undetectable viral load have effectively no risk of sexually transmitting the virus to an HIV-negative partner." The U=U (undetectable = untransmittable) campaign seeks to educate individuals, communities, and providers about the wealth of solid scientific evidence behind this HIV-prevention tool. 

This detailed FAQ was created in partnership with Prevention Access Campaign to help answer questions about U=U

Check out our U=U page aimed at providing basic knowledge about U=U for a wide variety of audiences. 

Viral load is the amount of HIV that’s found in a blood sample from a person living with HIV. Generally, the higher the viral load, the more likely HIV transmission can occur. Both  — “undetectable viral load” and “viral load suppression” — refer to extremely low measures of HIV and mean virtually the same thing.

More specifically:

  • Undetectable viral load: Daily HIV treatment can reduce a person’s viral load to the point where it cannot be detected by common blood tests. In the U.S., this means fewer than 50, 40, or even 20 copies of the virus in a blood sample, depending on the type of test.
  • Viral load suppression: When HIV treatment suppresses a personֽ’s viral load to less than 200 copies, this is called being “virally suppressed”. This measurement is used more often in international studies.


Being undetectable or virally suppressed improves the health of people living with HIV and prevents the sexual transmission of the virus. However, this does not mean the person is cured or the virus is gone from their body. Taking HIV treatment as prescribed and staying in care are important to maintaining an undetectable viral load.

No. In September 2017, the U.S. Health and Human Services confirmed there is “effectively no risk” of transmitting HIV to a sexual partner when a person with HIV achieves and maintains an undetectable viral load while on HIV treatment for six months or more. It is impossible to prove zero risk in science, but from a practical standpoint, experts agree the risk is zero.

no risk

The conclusion is based on the accumulated results of clinical research and real world experience including three large international studies (PARTNER, HPTN 052, Opposites Attract) and the 2008 Swiss Statement.

For instance, in PARTNER, there were zero transmissions out of 58,000 acts of condomless sex between people with HIV with undetectable viral loads and their HIV-negative partners (mostly heterosexual couples). In Opposites Attract, there were no transmissions out of 17,000 condomless sex acts between men who have sex with men. Since the advent of combination therapy, there have been no confirmed reports of anyone with an undetectable viral load sexually transmitting HIV.

Treatment as prevention (TasP) refers to any prevention method that uses HIV medications to decrease the risk of transmission to a sexual or needle-sharing partner, or from a mother to child. HIV treatment reduces viral load in blood, semen, and in vaginal and rectal fluids to very low levels, which in turn reduces HIV transmission. TasP is the foundation for U=U.

Nearly everyone who starts HIV treatment finds a drug regimen that works within six months. About one out of six people will need additional time to find the right treatment due to tolerance and adherence issues. Ongoing access to medical care, adherence to treatment and regular viral load monitoring are essential to maintaining an undetectable viral load.

“Blips” are small, transient increases in viral load between 50 and 1,000 copies while on HIV treatment. It’s typical for a blip resolve without a change in treatment. Viral load blips have not been shown to increase the transmission of HIV. Unless viral load blips happen more frequently, a single blip does not mean treatment isn’t working and is normally not of concern to providers.

Access to adequate healthcare, treatment, and viral load testing are serious barriers in many parts of the world. Some people who have access to treatment may choose not to be treated or may not be ready to start. Others start treatment but have challenges with adherence for various reasons such as stigma, mental health issues, substance use, unstable housing, difficulty paying for medications, hostile environments, drug resistance, and/or intolerable side effects.  

For people living with HIV who are not virally suppressed or undetectable, highly effective options line condoms and (in some parts of the world) PrEP can be used individually or together to prevent HIV. Everyone living with HIV regardless of viral load has the right to a full and healthy social, sexual, and reproductive life.

Regular viral load testing is recommended 2–4 times a year for people with stable undetectable viral loads. People with HIV who use this as an HIV prevention strategy should talk to their providers to see if more frequent testing is recommended.  

Scientists have found that an undetectable viral load in the blood achieved through daily HIV treatment normally corresponds with undetectable viral loads in seminal, vaginal and rectal fluids.

Occasionally, people with undetectable viral loads in the blood have HIV RNA and DNA in seminal, vaginal and rectal fluids but this has not been found to increase the risk of transmission. HIV RNA and DNA are genetic particles of HIV, but whole virus is required to cause infection. Further, studies show that HIV RNA and DNA are most commonly found soon after starting HIV treatment and are hardly seen after a year or more of having undetectable viral load in the blood.

Most people who take HIV medications do not have side effects, but they can cause side effects for some people. Most are mild, manageable and short-lived. Fortunately, there are many medications available today that people can take or switch to without serious side effects. If you experience side effects, discuss these with your healthcare provider.   

Knowing how an undetectable viral load prevents HIV transmission may be especially useful for people wishing to conceive a baby without using other insemination methods. An undetectable viral load also dramatically reduces the risk of transmission during pregnancy or breastfeeding. For more information on HIV and reproductive health, go to HIVEonline.org or TheWellProject.org.

That depends on your needs and preferences. Having an undetectable viral load, using PrEP and using condoms are HIV-prevention strategies that people can use alone or together. Using multiple strategies has additional benefits: reducing anxiety, preventing other sexually transmitted infections (STIs), preventing pregnancy, or adding protection should a partner with HIV not adhere to their treatment regimen. Condoms are the only method that helps prevent HIV, STIs and pregnancy. 

Having an undetectable viral load for at least six months and continuing to stay on medication means you are not putting your partner at risk. You may want to consider the pluses and minuses of disclosing for you and your partner. A partner may become upset if they learn about your status after sex, and this can cause hardship even when there is no risk of transmission. Also, it’s extremely important to keep in mind that many discriminatory HIV criminalization laws in some states and parts of the world require you to disclose your status, even when there is no risk of transmission. To learn more about the HIV criminalization laws in your state and country, visit Center for HIV Law and Policy and SERO Project

Just like you cannot tell if someone has HIV by looking at them, you also cannot tell if someone has an undetectable viral load. Whether or not you choose to trust your partner is a highly personal decision and is likely to depend on your sexual practices and relationship circumstances. People engaged in consensual sex are responsible for their own sexual health. In some circumstances, PrEP is an excellent option to empower yourself against HIV transmission without depending on information from your sexual partners.

No. U=U does not apply to HIV transmission through needle sharing. There is not yet enough research to draw this conclusion. 

Some medical providers are not up to date with the current science. Others agree with the science but are concerned about: 1) an increase in condomless sex among people with HIV which may result in an increase in other STIs; and 2) patients’ potential lack of understanding that maintaining an undetectable viral load requires excellent treatment adherence and monitoring.

If a person interrupts their treatment by choice or circumstances outside of their control, their HIV will likely rise to detectable and perhaps infectious levels. Some medical providers selectively choose to discuss this information only with patients and clients whom they judge are “responsible” (for example: monogamous and with a stable linkage to treatment) rather than directly address the concerns described above through education.

This FAQ is based on information from the following sources

NIAID at National Institutes of Health

NYC Department of Health

Prevention Access Campaign

In collaboration with     Prevention Access Campaign logo