In this section, a very brief overview is given. More detail can be found on other websites, notably Avert, THT and the NHS.



HIV can be transmitted in three main ways:

Other topics covered in this section are:

You can jump to any of these topics by clicking on the heading above.

Sexual Transmission

Someone can eliminate or reduce their risk of becoming infected with HIV during sex by choosing to:

  • Abstain from sex or delay first sex
  • Be faithful to one partner or have fewer partners
  • Condomise, which means using either male or female condoms consistently and correctly

This has been referred to as the “ABC” method, and is widely promoted in many parts of the world.

Numerous studies have shown that condoms, if used consistently and correctly, are highly effective at preventing HIV infection, and also at preventing the transmission of other sexually transmitted infections (STIs) such as gonorrhea, chlamydia and syphilis. There are many sites that give more information about safer sex.

Consistent and proper condom use remains an effective method of HIV prevention.

People who take ART daily as prescribed and achieve and maintain an undetectable viral load have effectively no risk of sexually transmitting the virus to an HIV-negative partner. This is often referred to as U=U…Undetectable equals Untransmittable.

The full U=U consensus statement can be read here.

Note that an undetectable HIV viral load prevents only HIV transmission to sexual partners. It does not protect against other STIs and pregnancy.

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Transmission Through Blood

Transfusion of blood or blood products infected with HIV is the most efficient of all ways to transmit HIV, and sadly, in the 1980s, many people in the UK became infected in this way. Haemophiliacs were supplied with blood products which had been contaminated with HIV. However, the chances of this happening today are very small indeed, since all blood and blood products used for transfusions are now screened for HIV.

The safety of medical procedures and other activities that involve contact with blood, such as tattooing and circumcision, can be improved by routinely sterilising equipment. An even better option is to dispose of equipment after each use, and this is highly recommended if at all possible.

People who share equipment to inject recreational drugs risk becoming infected with HIV from other drug users who have HIV. Methadone maintenance and other drug treatment programmes are effective ways to help people eliminate this risk by giving up injected drugs altogether. However, there will always be some injecting drug users who are unwilling or unable to end their habit, and these people should be encouraged to minimise the risk of infection by not sharing equipment. Needle exchange programmes have been shown to reduce the number of new HIV infections without encouraging drug use. These programmes distribute clean needles and safely dispose of used ones, and also offer related services such as referrals to drug treatment centres and HIV counselling and testing. Needle exchanges are a necessary part of HIV prevention in any community that contains injecting drug users.

Health care workers themselves run a risk of HIV infection through contact with infected blood. The most effective way for staff to limit this risk is to practise universal precautions which means acting as though every patient is potentially infected. Universal precautions include washing hands and using protective barriers for direct contact with blood and other body fluids.


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Mother-to-Child Transmission (MTCT)

01-mother-and-childHIV can be transmitted from a mother to her baby during pregnancy, labour and delivery, and later through breastfeeding. In many parts of the world, this is a major route of transmission for HIV. There are a number of things that can be done to help a pregnant woman with HIV to avoid passing her infection to her child. A course of antiretroviral drugs given to her during pregnancy and labour can greatly reduce the risk of the child becoming infected, and in the UK, instances of MTCT have fallen to virtually zero following the routine HIV testing at antenatal clinics. If  a pregnant woman is diagnosed late in her pregnancy, so that it is not possible to reduce the risk of transmission by using antiretroviral drugs, then a caesarean section (an operation to deliver a baby through its mother’s abdominal wall, which reduces the baby’s exposure to its mother’s body fluids) will probably be done. This procedure lowers the risk of HIV transmission, but is likely to be recommended only if the mother has a high level of HIV in her blood.

HIV can also be transmitted to a baby through the mother’s breast milk. The only certain way to avoid transmission if the mother is living with HIV is to abstain from breastfeeding and provide replacement foods (formula milk) for the baby.


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HIV Vaccine

In some instances, transmission can be prevented by means of a vaccine – for example, smallpox, hepatitis B and (to a lesser extent) flu transmission can be prevented (or significantly reduced) by administering an appropriate vaccine. Despite 30 years of research effort, no such vaccine for the prevention of HIV exists, and nor is such a vaccine likely to be developed anytime in the near future. It has proven to be extremely difficult to develop a vaccine for HIV; despite this, there are recent signs of progress, albeit slow. Work on a vaccine is continuing, and may yet be successful.


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UnknownA microbicide is something designed to destroy microbes (bacteria and viruses) completely, or else to reduce their ability to establish an infection. A microbicide for preventing HIV infection would be applied to the vagina or rectum to prevent the virus being passed on during sex. A microbicide would be especially useful for women unable to insist on their partner using condoms. They might be able to use a microbicide without their partners knowing. However, a microbicide would require regular reapplication, and so must be made into an inexpensive commodity that people will want to use regularly, such as a cream, gel or vaginal ring.

To date, an effective microbicide for HIV does not yet exist, and a lot of research is still being done in this area.

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Post-Exposure Prophylaxis (PEP)

imagesPEP is a course of treatment taken immediately after exposure that may prevent HIV infection after the virus has entered the body.

It is a course of anti-HIV medication that needs to be taken daily over the course of a month. The has been available since the early- to mid-1990s for health workers who have had ‘needle-stick’ or similar injuries – accidentally pricking themselves with a needle that has been used for someone with HIV, for example.

More recently, PEP has been made available to people who might have been exposed to HIV during sex. For the treatment to be effective, it needs to be started as soon as possible after exposure, and no later than 72 hours after exposure.

PEP can be available from sexual health clinics and hospital accident and emergency departments. Many people say they have had difficulty obtaining PEP from these places, especially outside metropolitan areas. You are more likely to be successful if you enquire at a sexual health clinic or A&E in a hospital where there is also a specialist HIV clinic.

You must also meet the prescribing guidelines for PEP – a series of questions will be asked to see whether or not there is a significant risk of HIV infection. Often, people may not know how HIV can be transmitted, so they may worry unnecessarily. In any event, if you are concerned, answer the questions openly and honestly, and then PEP can be given if appropriate.

PEP is not a cure for HIV and is not guaranteed to prevent HIV from taking hold once the virus has entered the body. Condoms for sex remains the most efficient way of staying safe from HIV.


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Pre-Exposure Prophylaxis (PrEP)

Unknown-1PrEP refers to a form of treatment that can be taken before exposure to a disease in an attempt to prevent infection. It is a course of HIV drugs taken by HIV negative people before sex to reduce the chance of getting HIV. Results in trials have been very successful, with PrEP significantly lowering the risk of becoming HIV positive and without major side effects. The medication used for PrEP is a tablet called Truvada, which contains tenofovir and emtricitabine (which are drugs commonly used to treat HIV).

There is a full guide to PrEP here.

PrEP is available on the NHS in Wales and Scotland.

PrEP will be available to 10,000 people in England as part of the IMPACT trial starting on 1 September 2017. NHS England expects sexual health clinics in London, Brighton, Manchester, Liverpool and Sheffield to be some of the first to start enrolling people in September, with more to follow in October.

For further information on the trial and to join, see the PrEP Impact Trial website or contact

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Criminal Transmission of HIV

This is a complicated and difficult subject, and only a brief overview will be given here. There is much more detailed information and discussion on a number of other websites, including:

Avert THT NAM Aidsmap

For the vast majority of people living with HIV, preventing others from acquiring HIV will of course be uppermost in their minds. Unfortunately, not everyone living with HIV takes all the precautions that perhaps they should or could, and there have been several stories in the UK about deliberate or reckless transmission of HIV to another person.  This has led to a number of arrests and prosecutions in the UK, using a very old piece of law that is perhaps not best suited for dealing with this modern situation. Also, it would appear that the police and judiciary – and a lot of the press – seem to know very little about HIV, or are still misinformed about HIV.

The situation as it stands today in the UK is that:

if someone has HIV

and they understand how HIV is stransmitted

and they had sex with someone who does not have HIV

and they did not disclose their HIV status beforehand

and they didn’t take reasonable precautions (that is, using a condom properly)

and the other person becomes infected with HIV

then they may be prosecuted for reckless transmission of HIV, and if found guilty, they may receive a custodial sentence. Whilst no-one would condone the deliberate and intentional transmission of HIV, most if not all prosecutions have been for reckless transmission, where intent is not a factor – just the conditions described above.

The law is still very complicated and confused in this area, and anyone who might be in this situation – either as someone who has transmitted HIV, or has acquired HIV – should seek professional advice, and should talk to NYAA or other support organisations as soon as possible.

Technically, even if HIV has been transmitted, it is very difficult (if not impossible) to prove that person A specifically gave the infection to person B – the scientific testing that exists does not allow this conclusion to be drawn. Furthermore, the entire sexual life and history of the person who has been infected will be probed and analysed, to see if realistically, the ONLY possible way they acquired HIV was from the person accused. In many cases, this may be difficult to prove conclusively.

Until these recent cases, it was always the case that every individual should assume responsibility for their own sexual health, and take appropriate precautions to protect themselves. This, though, is not the case with HIV – here, the entire responsibility has been placed on the partner who is living with HIV, whilst the other partner has (it would appear) no responsibility at all for their own health and welfare. This seems to be an inequitable position, but this is how the law stands at present in the UK – and in many other parts of the world as well. Indeed, in other parts of the world, the law is more draconian than in the UK – there have been prosecutions even when there has been no transmission of HIV.

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Treatment as Prevention (TasP)

Unknown-2Treatment as Prevention (TasP) refers to HIV prevention methods that use antiretroviral treatment (ART) to decrease the risk of onward HIV transmission. ART reduces the HIV viral load in the blood, semen, vaginal fluid and rectal fluid to very low levels (‘undetectable’ or “non-detectable” or “n/d”), reducing an individual’s risk of HIV transmission. Studies have shown that for someone with HIV who is on ART, and who has had an undetectable viral load for more than 6 months, there is effectively no risk of onward sexual transmission. This is often referred to as U=U.

TasP has been recognised as a valid reason for initiating ART in people who express significant concern about onward transmission.

Much more detail about TasP can be found here.

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