Recent studies have shown that people with diagnosed HIV, on medical treatment with an “undetectable viral load”, cannot pass the virus on to their sexual partners.

Undetectable 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.
  • Undetectable does not mean cured: the virus is still present in the bloodstream. But being undetectable means being uninfectious to other people.
  • Undetectable = Uninfectious (U=U).

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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 undetectable viral load 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 undetectable.

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.

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. This document soon became known as the ‘Swiss Statement’ and it 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 unifectious, 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 undetectable 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.

Undetectable = Uninfectious (U=U) is a major worldwide campaign that promotes awareness of this evidence, and its implications for HIV prevention. Find out more from the Prevention Access campaign.

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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