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Viral load and transmission – a factsheet for people with HIV

Gus Cairns
Published: 16 September 2015

The amount of HIV in your body fluids is called your viral load. Effective HIV treatment (antiretroviral therapy) suppresses the amount of HIV in your body fluids to the point where it cannot be detected by the tests used in clinics. Doctors call this ‘virological suppression’ but it is often known as ‘having an undetectable viral load’ or ‘being undetectable’.

Having an undetectable viral load does not mean you are cured of HIV. It does not mean you should stop taking treatment. It does mean that, as long as your viral load stays undetectable, you radically reduce your chance of passing HIV on to someone else.

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

Viral load at different stages

During the first few weeks after a person contracts HIV, viral load is usually very high – typically several million viral copies per millilitre of blood (copies/ml). There is a considerable risk of passing on HIV at this point, and many people acquire HIV from someone who has only recently acquired HIV themselves (and may not know it).

After this period of early infection, viral load usually drops. A typical viral load in someone not taking treatment may be 50,000 copies/ml. There is still a risk of passing HIV on.

When someone starts HIV treatment, viral load usually becomes undetectable within six months. The risk of HIV transmission is greatly reduced when people have an undetectable viral load.

The evidence

In 2011, a large scientific trial called HPTN 052 found that HIV treatment reduced the risk of passing on HIV to a regular heterosexual partner by 96%. The only reason it was not 100% is that one person in the trial did acquire HIV, but this happened just a few days before or after their partner started treatment.

A statement by the British HIV Association (BHIVA) and the Expert Advisory Group on AIDS (EAGA) said if the HIV-positive partner is on successful HIV treatment this is “as effective as consistent condom use” in limiting transmission. The statement stressed that regular viral load testing is vital and advised waiting six months after the first undetectable viral load test to be sure that treatment is working.

The BHIVA/EAGA statement only applied to vaginal sex because there were not enough gay couples in HPTN 052 to show whether HIV treatment reduced the risk to the same extent in anal sex.

In 2014, a study called PARTNER did not find a single HIV transmission in 16,400 occasions of sex between gay men and 28,000 between heterosexuals where the HIV-positive partner had a viral load below 200 copies/ml. In 2015, a similar study exclusively of gay male 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?

A lot of people with HIV see the reduction of infectiousness and relief from anxiety about transmission as very important benefits of HIV treatment. You may wish to take your viral load and your likely infectiousness into consideration when thinking about safer sex.

If you want to stop using condoms, it is important to discuss this carefully with your partners and ensure they are also comfortable with the decision. Discussing what an undetectable viral load means with HIV-negative partners may help reduce their anxiety about HIV transmission. But this information will probably be new to most people who do not have HIV; it may take time for someone to understand and trust what you are saying.  

Knowing how HIV treatment can reduce the risk of passing on the virus may be especially useful for people wishing to have a child. Couples in which one person has HIV and the other does not may consider having unprotected sex on days when the woman is ovulating and at her most fertile.

It is important to remember that while HIV treatment will protect your partners from your HIV, it does not protect them or you from other sexually transmitted infections (STIs). Also, in some countries, condomless sex without disclosing your HIV status is a criminal offence, regardless of the likelihood of HIV transmission.

If I start HIV treatment, how quickly will my viral load become undetectable?

It can take as long as six months. Until then you may still be infectious. It’s a good idea for you and your partners to wait until your viral load has been undetectable for at least six months before making any decisions about whether to stop using condoms – or for them to stop using PrEP (pre-exposure prophylaxis).

Does HIV treatment always work?

About one in six people on their first HIV treatment regimen either never have an undetectable viral load or their treatment stops working in the first year. During the second year on treatment, the chance of your therapy ceasing to work is about one in twenty and this declines further over the next decade to about a one-in-fifty chance of failure in any one year. So the longer you’ve been on a particular HIV therapy, the less likely it is to stop working. And almost everyone reduces their viral load to an undetectable level on their second or third regimen.

If someone’s treatment does not result in viral load becoming undetectable, this is usually because they are having problems taking their treatment as prescribed i.e. they don’t take all their pills at the right time, without missing doses.

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 if they had an undetectable viral load at the time HIV was transmitted.

Isn’t the viral load in semen, vaginal fluids or rectum more important than viral load in blood?

Viral load in blood and in other body fluids is usually very similar – if HIV in your blood is undetectable, it’s likely to be undetectable elsewhere. Occasionally people have undetectable HIV in blood and have low levels of HIV in other body fluids, but rarely at infectious levels.

What about sexually transmitted infections (STIs)?

If you are not on treatment, some STIs can make you more infectious: for instance, syphilis can double your viral load. HIV-negative partners are also more likely to get HIV if they have an STI. However, in the PARTNER study, there was not a single HIV transmission even though many people had STIs.

Viral load and transmission – a factsheet for people with HIV

Contact NAM to find out more about the scientific research and information used to produce this factsheet.

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.