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Undetectable Viral Load [U=U]

Māheahea te nui o te korakora huaketo

An undetectable viral load is when the amount of HIV in a person’s blood (their viral load) is no longer able to be detected by a standard viral load test for HIV. 

People living with HIV who are on antiretroviral treatment and maintain an undetectable viral load for at least six months do not sexually transmit HIV.

Research of gay and bisexual men who are living with HIV and have an undetectable viral load, and their HIV-negative partners in the Opposites Attract Study reported no cases of HIV transmission in almost 17,000 reported acts of anal intercourse without a condom.

These results support those of previous studies with similar findings and the Centers for Disease Control and Prevention (CDC) supports the notion that ‘Undetectable equals Untransmittable’ – also known as ‘U=U’.

The U=U message declares that because the HIV transmission risk is zero, PLHIV with a sustained undetectable viral load do not transmit HIV to their sexual partners.

On top of this, top line results of the PARTNER trial showed zero HIV transmissions in 22,000 occasions of sex between gay male couples where the HIV infected partner had an undetectable viral load.

While having an undetectable viral load means there is no risk of transmitting HIV, it will not protect from acquisition or transmission of other STIs like syphilis or gonorrhoea. Because of this, it's a good idea to keep condoms in the mix with casual partners and to have a regular sexual health check-up.

What does undetectable [U=U] mean?

Undetectable – or undetectable viral load – is when the amount of HIV in a person’s body (their viral load) is no longer able to be detected by a standard viral load test. A person living with HIV (PLHIV) who is diagnosed, on antiretroviral treatment (ART) and who achieves and maintains an undetectable viral load (UVL) for at least 6 months has no risk of sexually transmitting the virus to an HIV-negative partner.

However, the risk of other STIs remains.


u=u with people in people in the background

What does 'treatment as prevention' mean?

Treatment as prevention (TasP) refers to the use of HIV medication to reduce the risk of HIV transmission at a community level. If everyone living with HIV was diagnosed, started treatment immediately and was able to maintain an undetectable viral load, there would be no sexual transmission of HIV. In this way treatment would become a form of prevention. 


How long do I have to be on treatment before my viral load becomes undetectable?

It will be possible for most people diagnosed with HIV to reach an undetectable viral load within 3 to 6 months of starting treatment. However, if someone starts treatment very late and therefore has a low CD4 count, or they don’t take their pills as prescribed, then it will make reaching undetectable more difficult. It is important not to assume that everyone who is living with HIV will be able to reach or sustain an undetectable viral load.


Does having an undetectable viral load mean that HIV absolutely cannot be transmitted?

Based on the findings of new research into HIV transmission – including the PARTNER and Opposites Attract studies – we can now confidently say that if someone is able to obtain and maintain an undetectable viral load for at least 6 months, then there is no risk of passing on HIV through sex.

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The Science of Undetectable: 6 Insights

To trace the simple path from treatment to UVL, we spoke to Dr Sunita Azariah, a sexual health expert who has had patients living with HIV for more than 20 years.


What if I can’t get to undetectable?

Getting to undetectable might not be possible for everyone who is diagnosed with HIV, even if they take their medication as prescribed. It is important that people living with HIV are not pressured or expected to have an undetectable viral load.


How often should I have my viral load tested?

This is something you should discuss with your doctor. A basic guide to viral load testing is to have it done every 3 to 6 months. If, however, you are relying on being undetectable as your primary means of HIV prevention, you may want to consider testing your viral load more frequently. To find out more about this talk to your HIV specialist.


Featured FAQs

Do I still have to disclose my HIV-positive status even if my viral load is undetectable?


New Zealand law requires people living with HIV to take ‘reasonable precautions’ to avoid passing on HIV. The only case to ever come before the courts in New Zealand was for vaginal intercourse. It found that condoms are needed to be used as a precaution. That means that legally, if you are not using condoms during penetrative sex, you must disclose your HIV status. There has not been a case in New Zealand to test whether an undetectable viral load would be considered ‘reasonable precaution’.

If my viral load is undetectable, can I stop taking my meds?


No. Remaining on treatment is key to keeping your viral load under control and stopping the HIV virus from replicating. If you stop taking your medication even for a week or two, you give HIV the opportunity to replicate more quickly, increasing your viral load and the risk of developing resistance to your treatment.

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