Factsheet Viral load and transmission – a factsheet for HIV-negative people

Gus Cairns, Published September 2015

Key points

  • People with HIV who are on treatment and have an undetectable viral load are extremely unlikely to pass on HIV.
  • Large scientific studies have proven this.
  • Not everyone taking HIV treatment has an undetectable viral load.

When people with HIV take effective treatment, the amount of HIV in their body fluids (blood, semen, vaginal fluid, breast milk, and moisture in the rectum) falls drastically, to the point where it is highly unlikely they would pass HIV on to someone else.

The quantity of virus that someone living with HIV has in their blood can be measured, and this is called their ‘viral load’. When a person has very little virus, they are said to have an ‘undetectable’ viral load.

If someone has an undetectable viral load, it does not mean they are cured of HIV. If they stop taking HIV treatment, their viral load will become detectable again.

But having an undetectable viral load does mean that they are very much less likely to pass HIV on to someone else. In fact, most experts now agree that a person with a consistently undetectable viral load is uninfectious (cannot pass HIV on to another person).

This factsheet is written for people who don’t have HIV. This topic is also covered in a factsheet written for people who are living with HIV.

How do we know this?

In 2011, a large scientific trial called HPTN 052 found that if someone living with HIV started HIV treatment, their risk of passing HIV on to their regular HIV-negative partner fell by 96%. In 1763 couples, there were 28 transmissions from people not taking treatment and only one from someone who was. That transmission happened around the time the HIV-positive partner was starting treatment, before their viral load became undetectable.

A statement by the British HIV Association (BHIVA) and the Expert Advisory Group on AIDS (EAGA) said that successful HIV treatment is “as effective as consistent condom use” in preventing HIV transmission. The statement stressed that viral load needs to be tested regularly. It advised waiting six months after the first undetectable viral load test, to be sure that treatment is working.

This statement only applied to vaginal sex. This is because there were not enough gay couples in the HPTN 052 study to show whether HIV treatment had a similar effect during anal sex.

"Most experts now agree that a person with a consistently undetectable viral load is uninfectious (cannot pass HIV on to another person)."

In 2014, a study called PARTNER reported results on the risk of transmission when a person living with HIV has an undetectable viral load. There was not a single HIV transmission in 16,400 occasions of sex between gay men and 28,000 between heterosexuals. In 2015, a similar study of male gay couples, Opposites Attract, also found no transmissions from partners with an undetectable viral load. Both studies are collecting more data and will have final results in 2017.

What does this mean for me?

If you have a partner with HIV who is on treatment and has an undetectable viral load, the chances of them passing HIV on to you are either extremely low or zero.

Of course, using a condom reduces any remaining chance even further, but a lot of people prefer not to use condoms, especially in long-term relationships. If your partner has an undetectable viral load, they are extremely unlikely to pass HIV on – even if you don’t use condoms.

If you have a partner who has HIV and you do want to stop using condoms, taking their viral load into consideration, it is important to discuss this carefully with them and ensure you are both comfortable with this decision.

Instead of always using condoms, many people try to make sex safer by choosing partners with the same HIV status as them. This is sometimes called ‘serosorting’.

This can work for people with HIV (if their HIV status is certain). But HIV-negative people’s status is only certain up to the last time they took an HIV test. In casual situations especially, this may mean taking your partner's word for it or guessing their HIV status.

In a situation where a lot of people have HIV without realising it and where most people with diagnosed HIV are taking HIV treatment, having sex without a condom with partners who appear to be HIV-negative is not a safe strategy. It would be safer for HIV-negative people to have sex without a condom with partners who are HIV-positive and taking effective HIV treatment. But it is important to remember that while HIV treatment will stop your partners from passing on HIV, it does not protect you or them from other sexually transmitted infections (STIs).

Knowing how HIV treatment can reduce the risk of passing on HIV may be especially useful for people who want to have a baby. Couples in which one person has HIV and the other does not may consider having sex without a condom on days when the woman is ovulating and at her most fertile. Pregnancy can be achieved while keeping the risk of HIV transmission extremely low.

Does treatment always mean people have an undetectable viral load?

Not everyone taking HIV treatment has an undetectable viral load. After starting HIV treatment, it can take as long as six months for a person’s viral load to become undetectable. Until then they may still be infectious. A statement from British experts recommends that you and your partner should not make any decisions about stopping using condoms until their viral load has been undetectable for at least six months.

When starting HIV treatment, some people find that the first prescribed drugs don’t work well for them. But nearly everyone finds a combination that works and the risk of treatment failing declines over time.

Occasionally, someone who is taking treatment and has previously had an undetectable viral load finds that their viral load is detectable. Often, this is just a ‘blip’ and the viral load returns to normal at the next test. (It may just be a lab error.) Moreover, a detectable viral load below 1500 copies/ml is probably not infectious.

Do people with an undetectable viral load never transmit HIV?

It’s hard to prove that people with an undetectable viral load never transmit HIV. One study found that the lowest recorded viral load in someone who transmitted HIV was 362 copies/ml, though this person was not taking treatment. There have been three reports of transmissions involving gay men who had an undetectable viral load near the time of transmission, but we do not know whether their viral load was undetectable at the time HIV was passed on.

Even if your partner has an undetectable viral load, it is still a good idea to take an HIV test regularly as viral loads can occasionally go up.

What about sexually transmitted infections (STIs)?

STIs, especially herpes, can significantly increase your vulnerability to HIV. So if you have an STI, it increases your risk of acquiring HIV from someone who is not taking treatment. In addition, some STIs can make HIV-positive people who are not on HIV treatment more infectious.

However, in the PARTNER study, there were no HIV transmissions even though many people had STIs. It seems people on treatment usually continue to have an undetectable viral load even if they have STIs.

How else can I protect myself from HIV?

There are other ways to protect yourself from HIV, including using condoms, pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP).

This factsheet is due for review in September 2018

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This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.
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This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.