U=U (Undetectable = Untransmittable)

People living with HIV on medical treatment with an undetectable viral load cannot pass the virus on!

U=U facts:

  • The likelihood of passing on HIV is linked to how much virus someone has in their blood.
  • HIV medication – usually one or two pills per day – significantly reduces the level of HIV in a person’s bloodstream.
  • Most people on medication achieve an undetectable viral load which means they cannot pass the virus on.
  • Being undetectable does not mean cured: the virus is still present in the bloodstream. But being undetectable means being uninfectious to other people.

The scientific evidence for U=U can be found in the answer to our third frequently asked question below.

Frequently Asked Questions

Antiretroviral (ARV) HIV medication works by reducing the level of HIV in a person’s bloodstream (known as viral load). The viral load is said to be “undetectable” when the level of the virus in the blood of a person living with HIV is so low it cannot be measured.

It is important to note that undetectable does not mean cured as the virus is still present in their body. If they were to stop taking their treatment, or they failed to take the treatment every day as prescribed by their doctor, then HIV would start replicating again and their viral load would become detectable – increasing the infectious amount in their bodily fluids. But undetectable does mean that treatment is working and has stopped HIV from being replicated. In this case, the risk of passing on HIV to their partner is negligible.

You should talk to your doctor about a treatment plan and using U=U as a prevention strategy. Your viral load should be undetectable for at least six months before you trust U=U as your main prevention method. It’s also vital that you take your HIV treatment exactly as prescribed and attend your outpatient clinic regularly for ongoing viral load tests to make sure you remain U=U.

If your viral load does not become undetectable or it becomes detectable again after previously being undetectable, there are still plenty of other methods to prevent HIV transmission, such as condoms and PrEP.

It is important to remember that, although undetectable viral load prevents the sexual transmission of HIV, it does not protect against other STIs. Using condoms reduces the risk of STIs, in conjunction with regular testing and treatment.

Researchers confirmed at the 22nd International AIDS Conference in summer 2018 that the chance of any HIV-positive person with an undetectable viral load transmitting the virus to a sexual partner is scientifically equivalent to zero. The researchers said that ‘zero transmissions mean zero risk’. This announcement in turn means that we can be as confident now that undetectable gay men pose no risk of HIV transmission as we already were for heterosexuals.

The 22nd International AIDS Conference announcement took place on the tenth anniversary of the original ‘Swiss Statement’ in 2008.

The Swiss National AIDS Commission issued a statement for doctors about the impact ARV treatment had in reducing HIV transmission to the sexual partners of their positive patients in 2008 that became known as the ‘Swiss Statement’. The statement declared that an HIV positive person on effective HIV treatment, with an undetectable viral load, cannot transmit HIV through sexual contact.

The Swiss Statement cautioned that, for someone living with HIV to be uninfectious, they had to have good adherence.

Adherence means:

  • they must take their medication as prescribed
  • they must routinely see their HIV doctor
  • their viral load must be U=U for at least six months
  • they must have no sexually transmitted infections (STIs).

In the decade since the Swiss Statement, a number of important studies have produced evidence to support it:

  • In 2011, the HPTN-052 study found that medication dramatically reduced the risk of HIV transmission in sero-different (where one partner is HIV negative and the other is HIV postitive) heterosexual couples.
  • In 2016, the PARTNER study reported no HIV transmission among sero-different couples who had condomless sex more than 58,000 times.
  • In 2018, the PARTNER 2 study announces that zero transmissions mean zero risk.

Undetectable = Untransmittable (U=U) is a major worldwide campaign that promotes awareness of this evidence, and its implications for HIV prevention. Useful links to find out more about using U=U as an HIV prevention method:

Whether you use undetectable = uninfectious, or undetectable = untransmittable, both definitions essentially mean the same thing: someone with an undetectable viral load cannot pass on HIV to their sexual partner.

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Thanks for your understanding.

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