1. 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, HIV experts and health educators have described the transmission risk in public health communications as: "not transmittable", “no longer infectious”, "zero risk", "no infection risk", “do not transmit”, and “cannot transmit.”1  


2. What is an "undetectable viral load" and what is "viral load suppression"?

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.  Both "undetectable" and "viral load suppression" are extremely low measurements of HIV that are virtually the same. The terms are often used interchangeably in public health communications. 


  • Undetectable viral load:  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.  Excellence adherence, or taking ART as prescribed, is important to maintain an undetectable viral load.   


  • Viral load suppression: When ART suppresses a person's viral load to 200 copies/ml or less this is called being "virally suppressed." Being virally suppressed prevents the sexual transmission of HIV while simultaneously improving the health of a person living with HIV. 1 Studies show that when a person is virally suppressed they cannot transmit HIV to sexual partners. Excellence adherence, or taking ART as prescribed, is important to maintain viral suppression. 


For the purposes of the U=U campaign, the term "undetectable" is used synonymously with the term "virally suppressed."


3. 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.  Since the advent of combination therapy, there have been no confirmed reports of anyone with an undetectable viral load sexually transmitting HIV.11


4. 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 the risk is 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  


5. 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) and 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 and because treatment did not work properly for a small number of the participants. 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


6. 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 perinatally. 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. 

7. 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 need additional time to find the right treatment due to tolerance and adherence issues. Adherence to treatment and regular viral load monitoring are essential to maintaining an undetectable viral load. People who remain undetectable for a year or more with excellent adherence to treatment, are extremely unlikely to experience a viral rebound, known as ‘treatment or virological failure’.17Treatment failure after sustained viral suppression is rare and almost always related to poor treatment adherence.18


8. Do viral “blips” increase the chance of transmission?

Viral blips have not been shown to increase the transmission of HIV.1,6,7 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


9. 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.


10. Why do some people have detectable viral loads?

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 a variety of reasons such as stigma, mental health challenges, substance abuse, unstable housing, difficulty paying for medications, hostile environments, drug resistance, and/or intolerable side effects.20  Some people with low but detectable viral loads also cannot transmit HIV. For instance, someone who is virally suppressed (under 200 copies/ml) and still detectable (above approx 40 copies/ml depending on the test) cannot transmit HIV. The major studies on the subject were based on the risk of HIV transmission from people who were virally suppressed.1  For people living with HIV who are not virally suppressed or undetectable, there are highly effective options including condoms, and in some parts of the world, PrEP, which can be used individually or in combination to prevent HIV.  Everyone living with HIV regardless of viral load has the right to full and healthy social, sexual, and reproductive lives. 


11. How often should viral load testing be done?

Regular viral load testing for health benefits is normally recommended about 2-4 times a year for people who have a stable undetectable viral load.21 People with HIV who are using an undetectable viral load as an HIV prevention strategy should talk to their providers to see if increased viral load testing is recommended.  


12. What if there is detectable HIV in semen, vaginal or rectal fluids but not in the blood?  

Scientists have found that HIV treatment that leads to an undetectable viral load in the blood also normally leads to an undetectable viral load in semen, vaginal, and rectal fluids. Occasionally people with an undetectable viral load in the blood have levels of HIV in semen, vaginal and rectal fluids but this has not been found to increase transmission risk. Further, studies show that these levels are most common soon after starting HIV treatment and are hardly seen after a year or more of an undetectable viral load in the blood.22


13. Are there any side effects to being on HIV medicines?
HIV medicines can cause side effects for some people. Most are manageable. Fortunately, there are numerous HIV medicines available today that people can take without serious side effects. If you do experience any side effects it is important to discuss these with your healthcare provider.23 


14. What does this mean for me if I have HIV?
It means that if you are undetectable and stay on HIV treatment, you are likely to be much healthier than if you were not on treatment and no longer need to be constrained by fear of transmitting the virus to others during sexual experiences. However, as Gus Cairns writes in Viral load and transmission - a factsheet for people with HIV, “if you want to stop using condoms, it is important to discuss this carefully with your partners and ensure they are also comfortable with the decision. Discussing what an undetectable viral load means with HIV-negative partners may help reduce their anxiety about HIV transmission. But this information will probably be new to most people who do not have HIV; it may take time for someone to understand and trust what you are saying.”24 It is important to remember that while an undetectable viral load will protect your partners from your HIV, it does not protect them or you from other sexually transmitted infections (STIs) or prevent pregnancy.  


15. What does this mean for me if I don’t have HIV?
You need not be constrained by fear of acquiring HIV while your sexual partner is undetectable. As Gus Cairns writes in Viral load and transmission - a factsheet for HIV negative people, “If you do want to stop using condoms, it is important to discuss this carefully with your partner and ensure they are also comfortable with the decision.”26 It is important to remember that while an undetectable viral load will prevent transmission of HIV, it does not protect you or them from other sexually transmitted infections (STIs) or unwanted pregnancy.


16. What does this mean for reproductive health, such as pregnancy and breastfeeding? 

Knowing how an undetectable viral load prevents HIV transmission may be especially useful for people wishing to conceive a baby without using alternative insemination practices.25  An undetectable viral load also dramatically reduces the risk of vertical transmission - during pregnancy or breastfeeding. 


17. Should I stop using condoms and/or PrEP if I’m with someone who is undetectable?
Having an undetectable viral load, using PrEP and using condoms are all HIV prevention strategies that people can choose to use alone or in combination. We provide information about the latest science of HIV transmission so people with HIV and their partners can make informed decisions about what works for them. Some people may prefer to use several HIV prevention strategies for a variety of reasons such as to reduce transmission risk anxiety, to prevent other STIs, to prevent pregnancy, or if the partner with HIV has a history of inconsistent ART adherence. Condoms are the only method that helps prevent HIV, STIs, and pregnancy. 


18. Do I need to disclose my HIV status to my sex partner if I am undetectable?
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. There is no moral imperative to disclose when you are not putting your partner at risk. However, 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 sexual interaction and it can cause unnecessary interpersonal consequences even when there is no risk of transmission. Also, it’s extremely important to keep in mind that many discriminatory HIV criminalization laws exist in some states and parts of the world that require you to disclose your status, even when there is no risk of transmission.27,28 To learn more about the HIV criminalization laws in your state and country, visit http://www.hivjustice.net and http://seroproject.com/.


19. Can I trust that my partner is really undetectable?
Just like you cannot tell if someone has HIV by looking at them, you also cannot tell if someone has an undetectable viral load by how they look. Whether or not you choose to trust your partner is a highly personal decision and is likely to depend upon your sexual practices and relationship circumstances. People engaged in consensual sex are responsible for their own sexual health. In some circumstances, PrEP, https://www.silompulse.com/prep is an excellent option to empower yourself against HIV transmission without depending upon trust of your sexual partner.


20. Does U=U apply to transmission through needle sharing? 

U=U does not apply to HIV transmission through needle sharing. There is not yet enough research to draw a conclusion. 


21. Why isn’t my medical provider telling me this information?
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 they interrupt treatment by choice or circumstances outside of their control, their virus will likely rise to detectable 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.


Page last reviewed: August 17, 2019

Page last updated: August, 2019

Authors and References
Professor Carrie Foote, Indiana University-Purdue University Indianapolis, and Bruce Richman, Prevention Access Campaign.


This FAQ is based on information from the following sources:


  1. Prevention Access Campaign. Undetectable=Untransmittable Primer Consensus Statement. 2016;http://www.preventionaccess.org/consensus Accessed Sept. 7, 2016.

  2. CDC.gov. Living with HIV. 2016; http://www.cdc.gov/actagainstaids/basics/livingwhiv.html. Accessed 10/25/16.

  3. Cohen MS, Chen YQ, McCauley M, et al. Antiretroviral therapy for the prevention of HIV-1 Transmission. New England Journal of Medicine. 2016;0(July 18):1-10. http://www.nejm.org/doi/full/10.1056/NEJMoa1600693#t=article

  4. Del Romero J, Castilla J, Hernando V, Rodríguez C, García S. Combined antiretroviral treatment and heterosexual transmission of HIV-1: cross sectional and prospective cohort study. British Medical Journal. 2010;340:c2205.http://www.bmj.com/content/bmj/340/bmj.c2205.full.pdf

  5. Frieden TR, Foti KE, Mermin J. Applying Public Health Principles to the HIV Epidemic—How Are We Doing? New England Journal of Medicine. 2015;373(23):2281-2287. http://www.nejm.org/doi/full/10.1056/NEJMms1513641#t=article

  6. i-Base. Q&A on the PARTNER study: how to interpret the zero transmission results. 2016; http://i-base.info/qa-on-the-partner-study/. Accessed 07/18/2016.

  7. Loutfy M, Tyndall M, Baril J-G, Montaner JS, Kaul R, Hankins C. Canadian consensus statement on HIV and its transmission in the context of criminal law. Canadian Journal of Infectious Diseases and Medical Microbiology. 2014;25(3):135-140.http://www.hivlawandpolicy.org/resources/canadian-consensus-statement-hiv-and-its-transmission-context-criminal-law-mona-loutfy

  8. Loutfy MR, Wu W, Letchumanan M, et al. Systematic review of HIV transmission between heterosexual serodiscordant couples where the HIV-positive partner is fully suppressed on antiretroviral therapy. PloS one. 2013;8(2):e55747.http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0055747

  9. Rodger AJ, Cambiano V, Bruun T, et al. Sexual activity without condoms and risk of HIV transmission in serodifferent couples when the HIV-positive partner is using suppressive antiretroviral therapy. Journal of the American Medical Association. 2016;316(2):171-181. http://jama.jamanetwork.com/article.aspx?articleid=2533066

  10. Vernazza P. HIV-infizierte Menschen ohne andere STD sind unter wirksamer antiretroviraler Therapie sexuell nicht infektiös. 2008.http://www.aids.ch/de/downloads/pdfs/EKAF-Statment_2008-05-089.pdf

  11. Vernazza PL, Bernard EJ. HIV is not transmitted under fully suppressive therapy: The Swiss Statement – eight years later Swiss Med Weekly 2016; http://bit.ly/SwissMedWeekly  Accessed Sept. 4, 2016, 146.

  12. AIDS Vancouver. In the News: Dr.  Julio Montaner’s TED Talk HPTN052 and What it Means to Be Undetectable. 2016;http://www.aidsvancouver.org/hiv_in_the_news. Accessed July 31, 2016.

  13. Cohen MS, Chen YQ, McCauley M, et al. Prevention of HIV-1 infection with early antiretroviral therapy. New England Journal of Medicine. 2011;365(6):493-505. http://www.nejm.org/doi/full/10.1056/NEJMoa1105243#t=article

  14. Centers for Disease Control and Prevention. Prevention Benefits of HIV Treatment. 2015;http://www.cdc.gov/hiv/research/biomedicalresearch/tap/index.html. Accessed July 31, 2016.

  15. Avert. Treatment as Prevention (TasP). 2016; http://www.avert.org/professionals/hiv-programming/prevention/treatment-as-prevention#footnote31_k7sbn1z. Accessed 06/23/16.

  16. O'Connor J, Smith C, Lampe F, Johnson M, Sabin C, Phillips A. Rate of viral load failure over time in people on ART in the UK Collaborative HIV Cohort (CHIC) study. Journal of the International AIDS Society. 2014;17(4).http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4224895/pdf/JIAS-17-19527.pdf

  17. NAM. Factors affecting stable blood plasma undetectable viral loads. HIV Transmission and Testing Guide ND;http://www.aidsmap.com/Factors-affecting-stable-blood-plasma-undetectable-viral-loads/page/2802817/. Accessed June 30, 2016.

  18. Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the Use of Antiretroviral Agents -Virological Failure. 2014; https://aidsinfo.nih.gov/guidelines/html/1/adult-and-adolescent-arv-guidelines/458/plasma-hiv-1-rna--viral-load--and-cd4-count-monitoring.  Accessed June 30, 2016.

  19. NAM. Viral Blips. Treatment Directory ND; http://www.aidsmap.com/Viral-blips/page/1729801.Accessed June 30, 2016.

  20. Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents- Limitations to Treatment Safety and Efficacy Adherence to Antiretroviral Therapy. 2014;https://aidsinfo.nih.gov/guidelines/html/1/adult-and-adolescent-arv-guidelines/30/adherence-to-art. Accessed June 30, 2016.

  21. Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents - Viral Load Testing. 2014; https://aidsinfo.nih.gov/guidelines/html/1/adult-and-adolescent-arv-guidelines/458/plasma-hiv-1-rna--viral-load--and-cd4-count-monitoring. Accessed June 30, 2016.

  22. Mykhalovskiy E, Betteridge G, McLay D. Scientific research on the risk of the sexual transmission of HIV infection on HIV as a chronic and manageable infection. In, HIV Non-Disclosure and the Criminal Law: Establishing Policy Options for Ontario, 2010 (cited section updated 2013).  2013; http://www.aidslaw.ca/site/wp-content/uploads/2016/02/McLay2010_update-2013-Final.pdf. Accessed September 4, 2016.

  23. AIDSinfo.gov. Fact Sheet: Side Effects of HIV Medicines: HIV Medicines and Side Effects. 2016;https://aidsinfo.nih.gov/education-materials/fact-sheets/22/63/hiv-medicines-and-side-effects. Accessed June 30, 2016.

  24. Cairns G. Viral Load and Transmission - a Factsheet for People with HIV. 2015; http://www.aidsmap.com/Viral-load-and-transmission-a-factsheet-for-HIV-negative-people/page/2989764/. Accessed 06/23/16.

  25. Bujan L, Pasquier C. People living with HIV and procreation: 30 years of progress from prohibition to freedom? Human Reproduction. 2016;31(5):918-925.

  26. Cairns G. Viral Load and Transmission - a Fact Sheet for HIV-Negative People. 2015; http://www.aidsmap.com/Viral-load-and-transmission-a-factsheet-for-people-with-HIV/page/1044617/. Accessed 06/23/16.

  27. AIDSlaw.com. HIV Disclosure to Sexual Partners - An Overview. Resource Kit for Service Providers 2015; http://www.aidslaw.ca/site/wp-content/uploads/2014/02/Chapter2-ENG.pdf. Accessed June 30, 2016.

  28. Human Rights Campaign. What do I do If? 2016; http://www.hrc.org/whatdoido. Accessed August 1, 2016.

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