Most Londoners living with HIV have an ‘undetectable viral load’. In short, this means they cannot pass the virus on to their sexual partners.

What does Undetectable mean?

People with diagnosed HIV take medication to control the virus and its impact on their health. The majority of people in London on treatment have a consistently Undetectable viral load. This means the virus cannot be transmitted to a sex partner.

What is the viral load?

Viral load is the amount of the virus present in someone’s blood. The higher the viral load, the more infectious someone is.

Treatment for HIV

Antiretroviral therapy (ART) is used to treat HIV. Medication comes in the form of tablets, which need to be taken every day. They work by preventing the virus from being able to replicate in the body which allows the immune system to repair itself and prevent further damage.

The aim of HIV treatment is to reduce someone’s viral load to undetectable levels. This does not mean the virus has gone completely, it means the amount of HIV is minimal and cannot be detected by current tests. HIV blood tests are given per millilitre of blood and, in general, an undetectable result means there are fewer than 50 copies per ml.

It is important to note that being undetectable is not the same as being cured because the virus is still in the body and the viral load will increase if the medicine is not followed as prescribed. There is still no cure for HIV.

What does U=U and (TasP) mean?

U = U means Undetectable = Untransmissible

This sums up the fact that people with an undetectable viral load cannot transmit the virus to their sexual partners.

TasP = Treatment as Prevention

This is a different way of describing the same concept: that people living with HIV on correct treatment who are virally supressed cannot pass the virus on. In this way, treatment for HIV also acts as a method of viral prevention.

How to get tested

Buy low-cost condoms

How to get PrEP

Treatment as prevention

Frequently Asked Questions

No. There is no cure for HIV. But there are very effective antiretroviral therapies (ART) that allow most people with the virus to live a long and healthy life. Undetectable viral load means the medication has reduced the virus in someone’s to such an extent that it cannot be passed on to sexual partners.

Yes. When someone starts treatment, it can take a number of weeks or months for the medication to do its job in bringing HIV infection under control. Once the viral load is reduced to undetectable levels (under 50 copies/ml) it will stay this way through ongoing treatment as prescribed. HIV positive patients will attend regular outpatient clinics for ongoing viral load blood tests and expert medical care

No. 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 for any infections.

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. It was concluded  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.

Importantly, 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’. This statement effectively 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 positive) 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 = Untransmissible (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: