U=U: Undetectable = Untransmittable, and Do You Still Need Condoms?

"Doctor, I have been on medicine for two years and my virus has been undetectable the whole time. Am I still a danger to my partner?" I hear this question very often, and the answer I can give with confidence, based on the evidence, is no. If you keep your virus controlled, you do not pass HIV on through sex. This principle is called U=U, and it is one of the best pieces of news in the HIV field in decades.

What is U=U?

U=U stands for Undetectable = Untransmittable. It means that a person with HIV who takes antiretroviral treatment consistently, until the amount of virus in their blood (viral load) is too low to detect, and keeps it there, does not pass HIV to sexual partners, even without condoms.

In its 2023 policy brief, the World Health Organization (WHO) set out clear levels:

< 200 copies/mLUndetectableZero risk

200–999SuppressedAlmost zero, or very low

≥ 1,000 copies/mLNot yet suppressedRisk exists; treatment needs review

Low virusHigh virus

Based on WHO policy brief (2023). Stay undetectable for at least 6 months before relying on U=U.

Where does the evidence come from?

U=U is not just an opinion. It comes from large studies that followed couples where one partner has HIV and the other does not (serodiscordant couples) for years:

• HPTN 052 (published in the NEJM in 2011 and 2016) found that early treatment reduced transmission in heterosexual couples by more than 90%, and no transmission occurred when the partner with HIV was virally suppressed.
• PARTNER (JAMA 2016) and PARTNER2 (Lancet 2019) followed heterosexual and gay male couples who had condomless sex tens of thousands of times in total. Not a single transmission occurred when the partner with HIV had an undetectable viral load.
• Opposites Attract (Lancet HIV 2018), in gay male couples in Australia, Thailand and Brazil, found the same result.
• A systematic review in the Lancet in 2023 (Broyles and colleagues) confirmed that no sexual transmission was found when the viral load was below 1,000 copies/mL.

Today the WHO, the US CDC, UNAIDS and the health authorities of many countries, including Thailand, endorse U=U.

Conditions to meet before saying "I am U"

1. Take your medicine every day, consistently. Frequently missed doses can let the virus come back within a few weeks.
2. It takes time. Most people become undetectable within 1–6 months of starting treatment. The usual rule is to stay undetectable for at least 6 months before relying on U=U as a couple's main prevention method.
3. Confirm with viral load tests as scheduled, rather than guessing from feeling well.
4. If there is a period of missed medicine or serious illness, or a viral load result becomes detectable again, go back to using condoms or have your partner use PrEP until you have confirmed you are undetectable again.

What U=U does not cover

• Other sexually transmitted infections, such as syphilis, gonorrhea, chlamydia, herpes and HPV. HIV medicine does not prevent these. (Read Common sexually transmitted infections.)
• Unplanned pregnancy
• Breastfeeding. There is not yet enough data to say the risk is zero, so in Thailand formula feeding is still recommended instead. (Read HIV and having children.)
• Sharing needles or injecting equipment still carries a risk. They should never be shared.

Covers

• Sexual transmission of HIV
• When undetectable consistently
• And medicine is taken daily

Does not cover

• Other STIs: syphilis, gonorrhea, herpes, HPV
• Unplanned pregnancy
• Breastfeeding (Thailand advises formula)
• Sharing needles or injecting equipment

vs

Evidence from HPTN 052, PARTNER, PARTNER2 and Opposites Attract.

So do you still need condoms?

My answer is: "You do not need them to prevent HIV if you are truly U, but they are still worth using to prevent other infections", especially in these situations:

• A new partner, or more than one partner
• You have not yet been tested together for other sexually transmitted infections
• You do not want a pregnancy and are not using other contraception
• The partner with HIV has just started treatment, or their latest viral load was still detectable
• Your partner still does not feel confident, a feeling that matters and deserves respect

For couples in a long-term relationship who test regularly together, where the partner with HIV keeps the virus controlled, choosing not to use condoms is an evidence-based option. People who get syphilis or gonorrhea repeatedly may want to talk to a doctor about Doxy-PEP as well.

Why U=U matters in real life

U=U is not just a medical fact. It reduces guilt, fear and stigma. Many people with HIV used to think of themselves as "dangerous" to the people they love. U=U lets them have love and sex with dignity, and it encourages people to test and start treatment, because treatment is prevention at the same time.

How I can help

At Dr. Kris Clinic in Surat Thani, I support both people with HIV and their partners: explaining viral load results, planning prevention that suits your relationship, testing for other sexually transmitted infections together, providing PrEP for HIV-negative partners, and counseling couples when worries linger. Consultations are private, at the clinic or online anywhere in Thailand, and English-speaking consultations are available.