Undetectable Viral Load and HIV Transmission

Viral load is the term used to describe the levels of HIV in the body at any one time. It is determined through a blood test.

A higher viral load is associated with a higher risk of HIV transmission.  With successful HIV treatment, the viral load can become ‘undetectable’.  For many people on long term HIV treatment, with an undetectable viral load, the risk of transmitting the virus to a partner(s) is zero.

People living with HIV can now feel confident that if they have an undetectable viral load and take their HIV medications properly, they will not pass on HIV to sexual partners.

What is an undetectable viral load?  The amount of HIV in the blood of someone who has HIV is called their viral load.  Without HIV medication, the viral load can be high.  HIV medication stops HIV from making copies of itself, and the viral load can be made so low that it is not detectable in a standard blood test.  This is called having an ‘undetectable viral load’.

What about other body fluids like semen, vaginal fluids and rectal fluids? The viral load in blood and in other body fluids is usually very similar.  If HIV in your blood is not detectable, it’s likely to be very low or undetectable in other body fluids.

And what does untransmittable mean? It simply means that something cannot be passed on or transmitted.

When we are talking about HIV, undetectable = untransmittable means that when a person with HIV has a viral load that is not detectable, they cannot pass on HIV through sex.

The Science: A number of major studies took place to look at undetectable viral loads and the sexual transmission of HIV.  The biggest one was the PARTNER Study.

The PARTNER Study 
548 heterosexual couples


340 gay male couples

One person was HIV-positive with an undetectable viral load.

One person was HIV-negative.

Couples had anal and vaginal sex over 58,000 times with no condoms, no PEP and no PrEP. Zero cases of HIV being passed on.



That’s ZERO.  NoneNot a single case of HIV transmission.

The science is clear: Undetectable means Untransmittable.




So what does this mean if I am HIV-positive? Having an undetectable viral load not only stops HIV being passed on through sex, it is also good for your health.  In Ireland, and worldwide, it is now recommended that everyone diagnosed with HIV starts treatment as soon as possible.  The benefits of this, such as keeping your immune system strong and preventing illness, means that people can expect to live long, healthy lives.

It also means that if you keep taking your HIV medication properly, and keep your viral load undetectable, you can have sex without the worry that you might pass HIV on to your sexual partners.

Can I stop using condoms?  The science is very clear about the risk of passing on HIV through sex:  if you are HIV-positive with an undetectable viral load and are having sex without condoms with someone who is HIV-negative, the risk of passing on HIV is zero.

There are a few things to consider, however, when making a decision to stop using condoms:

  • For people with HIV, it generally takes about six months after starting HIV medication for the viral load to become undetectable. It is recommended that you keep your viral load undetectable for at least another six months before you decide to stop using condoms.  You should get regular viral load tests at your HIV clinic and make sure to ask the nurse or doctor for the results.
  • You should of course always discuss your wish to stop using condoms with your partner or partners and make sure they are comfortable with the decision. Remember, you should never feel pressured to have sex without a condom if you don’t want to, and equally you should never pressure someone else to either.
  • Having an undetectable viral load only stops HIV from being passed on. It does not stop other STIs from being passed on.  Using condoms is the best way to stop you from getting or passing on STIs such as chlamydia, gonorrhoea or syphilis.

Does the U=U message apply to HIV being passed on through needle sharing?

No.  Taking HIV medication will reduce the viral load, but there is not yet enough research to confidently say that HIV will not be passed on through needle sharing if the viral load is undetectable.  If you are an injecting drug user, the best way to stop yourself from getting or passing on HIV, is not to share needles or other drug using equipment.

Read more about U=U at www.preventionaccess.org