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What are HIV and AIDS?

Updated: Mar 6, 2023

HIV (human immunodeficiency virus) is a virus that attacks the immune system and leads to a life-threatening disease: AIDS (acquired immunodeficiency syndrome).

This article is pending medical review.


Written by Yasemin Kaya

Reviewed by Sophie Oppelt and Alizeh Ahsan

Edited by Juliëtte Gossens


HIV is a virus that attacks the immune system (1). Normally, the immune system helps our body fight off all kinds of microbes and infections and prevent us from getting severely ill. However, HIV attacks the cells of the immune system. This means people infected with HIV are more at risk for different diseases like lung infection, tuberculosis and even certain types of cancer.

The words HIV and AIDS are often used together and interchangeably, but they’re not the same thing. HIV is the virus that causes AIDS. AIDS is the result of the viral infection: extremely low levels of immune cells (most importantly the white blood cells). It’s one of the most important causes of death worldwide (17).

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Who Can Get HIV or AIDS?

According to the World Health Organisation (WHO), there were 1.5 million new HIV infections across the world in 2021 (14). The virus is especially common in Africa: two thirds of all new infections were in that region. In 2021, 38.4 million people were living with the infection (they are said to be HIV-positive) and unfortunately there were an estimated 650 thousand deaths due to AIDS in that year. Since the early 1980s, the disease has claimed at least 40 million lives – though it’s likely it’s a lot more than that. That’s because cases may be underreported due to the stigma associated with HIV and AIDS. In many places in the world, HIV-positive people face danger if other people know they’re infected (3, 15, 16).

Many people believe that only certain groups of people can get HIV, such as gay men. However, anyone can be infected with HIV, and it’s important to protect yourself when you’re having sex with others. You can read more about ways to protect yourself here. That said, we see that certain groups of people are more at risk, mostly due to their social and economic circumstances (3). These include:

- Men who have sex with men

- People who inject drugs (such as heroin) into their bloodstream

- Prisoners

- Sex workers

- Transgender people

Why are men who have sex with men and transgender people more at risk of HIV?

Again, even if you don’t belong to any of these groups, you’re definitely not protected from HIV infection. You can still get it if you’re not having safe sex, even if you’re heterosexual and cisgender. In fact, new HIV infections in the UK affect people who have heterosexual sex and men who have sex with men in a nearly 50-50 split (20).

How HIV Progresses

A HIV infection goes through three different stages, with the development of AIDS as the last stage.

First phase: acute

When people are newly infected, they often have flu-like symptoms: fever, sore throat, night sweats and fatigue are common in the first (acute) phase of the disease. Because these complaints are very common in all kinds of diseases, it’s difficult to recognise HIV infection early on. These symptoms typically go away within two weeks (2). During this period, the number of HIV particles in the blood (the so-called viral load) is very high. This means it’s easy to transmit the infection to another person if you’re having unprotected sex or sharing needles, for example. Read more about ways HIV is transmitted below.

Second phase: chronic

During the second phase of the disease, the virus is multiplying in the body. The viral load increases progressively over time as the virus attacks the immune cells. This is a cycle: as the virus attacks, the immune system can fight the virus less well because its ‘soldiers’ (the white blood cells) are infected. In turn, this allows the virus to multiply more. But this doesn’t cause any symptoms for a long time, and the flu-like symptoms of the acute phase have disappeared. That’s why this stage is often called the asymptomatic (meaning without symptoms) stage: you don’t even notice what’s happening in your body. This stage can take a long time (up to 10 years without treatment), during which your white blood cell count goes down steadily (2). That’s the root cause of the development of AIDS.

Third phase: AIDS

In the third phase, a HIV-infected person progresses to AIDS. This is the life-threatening end stage of the disease. It’s life-threatening because your immune system has been weakened by the HIV virus, to the point where it can’t fight off even the weakest microbes. There are also high levels of HIV in the blood (high viral load), which means the disease can be transmitted to other people easily (see below). This phase can last up to three years if not treated. Eventually, AIDS leads to such severe infections that it causes death (2).

How Is HIV Transmitted?

HIV can be transmitted (meaning it infects another person) when the blood, sperm, pre-semen (‘pre-cum’) or vaginal fluids of the infected person come into contact with somebody else’s blood, open wounds, or mucosal tissues (in the mouth, vagina, and the anal canal). There are four main ways HIV is spread from one person to another (4):

- Sex: HIV can be transmitted by anal and vaginal sex. However, due to certain aspects of the anal canal, the risk of infection is ten times higher during anal sex compared to vaginal sex. Especially when there are wounds or rashes in the genital area (for example due to other sexually transmitted diseases), the risk of passing on the virus is high.

o The risk of transmission during oral sex with a penis is incredibly low (19), though it might happen if the person using their mouth has open sores in their mouth. To ensure you’re protected, use an outside condom

o The risk of transmission during sex between two or more people with a vagina is also incredibly low. There are only a few reports of it ever happening (19).

- Needle sharing: in hospitals where there is no proper sterilization of used injection equipment (for example in some low-resource areas), this way of transmission plays an important role. This also applies if you’re using needles to inject drugs, and you’re sharing those needles with other people. This is why it's recommended that your doctor screens you for HIV when you come in for a check-up if you inject drugs (21).

- Mother to child: the HIV virus can be passed on from the mother or birthing parent to the child during pregnancy, birth, and breastfeeding. As you can read below, there are medications available that can prevent this transmission.

- Blood transfusions: today, donated blood is checked for contamination with HIV, hepatitis, and other disease-causing viruses and bacteria. But a few decades ago, this didn’t happen routinely – meaning many people who received blood transfusions during that time got infected with HIV because they received contaminated blood. This still sometimes happens (19), though it's very rare.

It’s important to note that HIV does not spread via coughing, sneezing or through the air (5). It is perfectly possible to share a household with an infected person and use the same dishes and toilets. Physical touch, such as giving hands, kissing and hugging can't transmit the disease either. You’re at risk only when you’re coming into close contact with somebody’s blood, sperm, pre-cum or vaginal fluids.

Fortunately, there are ways to make it nearly impossible for an HIV-positive person to spread the infection to another person, even if they’re having unprotected sex. Read more about this below.

How HIV Is Diagnosed

When your healthcare provider suspects you might have been infected with HIV, they can use a couple of different tests to make this diagnosis.

Currently, the European guidelines for HIV testing recommend an antigen-antibody test as the first choice (7). For this test, a healthcare professional draws some of your blood from a vein. That’s then sent to a lab. Antigen and antibody levels are then measured in the blood. Part of the HIV particle is the antigen, and our body reacts to the infection by producing antibodies that are specific for this antigen (8). These antibodies usually help clear out the microbes, but in the case of HIV, they are not effective enough to do so. A HIV-infected person will therefore have both HIV antigen and antibodies against HIV in their blood.

The major advantage of this test is that it can detect HIV in the first (acute) phase, when you’ve just been infected. It’s also a very reliable test, with a high sensitivity and specificity. If this test is positive, a different test (called an antibody differentiation assay) is done to see what type of HIV is present. This can influence the treatment that your doctor advises.

The downside of the antigen-antibody test is that it requires specific materials and techniques, which might not be accessible in a low-resource area (5). The test also needs blood, which means it has to be done in a professional healthcare setting. A different option that doesn’t require many resources or blood is the rapid HIV test (9). These rapid tests measure antibody levels in blood (from a finger stick, not from your vein) or even fluids from the mouth. This test can be done at home or low-resource healthcare facilities and gives a result in 20 to 40 minutes. However, a rapid test is less reliable than the antibody-antigen test and it can’t detect the infection in the acute phase.

How HIV Can Be Prevented

Currently, there is no cure for HIV. But once diagnosed, it can be managed with medication (see below). Diagnosing HIV and controlling it with medication are the most important and effective ways to prevent transmission and development into AIDS.

But there are several ways you and your doctor can help prevent HIV infection in the first place. These include:

- Condom use: although perfect use of condoms completely prevents HIV transmission, it’s difficult to use a condom perfectly (read more about proper use here). That’s why condoms are around 80 percent effective in protecting against HIV transmission. This means that in 80 out of 100 sexual intercourses with an HIV-positive person, the condom protects against HIV infection (10).

- Prevention of mother-to-child transmission: HIV can be transmitted from mother or birthing parent to child during pregnancy, birth and breastfeeding. However, when the pregnant person is taking medication to manage their infection, the amount of virus in the blood is low. This nearly always prevents transmission (11).

- Medical circumcision: medical circumcision of the penis can reduce the transmission of HIV between 50 to 60 percent (12). This is because there are a lot of immune cells in the foreskin of the penis, which are attacked by HIV. If you remove the foreskin, HIV has fewer cells to latch on to. During the initial healing phase, transmission is much more likely because it’s a fresh wound. Once the wound is properly healed, circumcision is considered an important part of HIV prevention.

It’s important to note that this applies mostly to heterosexual situations, and that it protects mainly the male partner or the person with the penis (19). The effect of circumcision for men who have sex with men is unclear.

- Post-exposure prophylaxis: even if you’ve already been exposed to HIV (“post-exposure”), it’s possible to prevent infection if treatment is started within 72 hours after this exposure (2). Examples of exposures include unprotected sex with an HIV-positive person, a needle stick accident in healthcare, or blood contact with an HIV-positive person. In these cases, or other situations in which there’s a risk of HIV exposure, you can be given a medication preventatively (this is what prophylaxis means) so that you’re not infected. Typically, you’ll have to take this medication for around 4 weeks. So: if you think you could have been exposed to HIV, contact your doctor or a sexual health clinic as soon as possible.

- Pre-exposure prophylaxis (PrEP): some people have a higher risk of getting infected, for example if they’re in the groups mentioned above. In these cases, it might be useful to take medication preventatively, before you’ve even been exposed to HIV (“pre-exposure”). Taking this medication as prescribed (taking it every day, on time) can reduce your risk of HIV infection by around 86 percent in case you’re exposed (13). But it’s often difficult for people to consistently take the medication, so the risk reduction is typically lower.

If you think you might benefit from PrEP (for example because you regularly engage in anal sex with different partners, or because you inject drugs), contact your doctor to ask about the possibilities.

Living With HIV

Although HIV can't be cured yet, it can be managed with medication. These drugs – called

antiretroviral drugs (ART) - keep a HIV-positive person in the asymptomatic stage of the infection. ART also prevents the HIV particles from multiplying, so the viral load is kept low (6). The goal is to keep the viral load so low, that it’s undetectable in the blood. This greatly reduces the risk of transmission in case somebody else is exposed to the HIV-positive person’s blood, sperm, pre-cum or vaginal fluids. People infected with HIV can then live life as normal without having to worry about transmitting the infection, if they take their medication consistently and their viral load is undetectable.

The medication can unfortunately not completely clear out the virus. This means that as soon as you stop taking it, or you’re not taking it consistently, the virus can multiply again. It can even become resistant against the medication, so it won’t work as well. You then run a higher risk of disease progression towards AIDS, and you’re more likely to transmit the infection.



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  3. Joint United Nations Programme on HIV/AIDS (UNAIDS). UNAIDS report on the global AIDS epidemic 2013. Available from: [Accessed November 27th, 2022]

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  12. Bailey RC, Moses S, Parker CB, Agot K, Maclean I, Krieger JN, et al. Male circumcision for HIV prevention in young men in Kisumu, Kenya: a randomised controlled trial. Lancet. 2007;369(9562):643-656. DOI: 10.1016/S0140-6736(07)60312-2

  13. McCormack S, Dunn DT, Desai M, Dolling DI, Gafos M, Gilson R, et al. Pre-exposure prophylaxis to prevent the acquisition of HIV-1 infection (PROUD): effectiveness results from the pilot phase of a pragmatic open-label randomised trial. Lancet. 2016;387(10013):53-60. DOI: 10.1016/S0140-6736(15)00056-2

  14. WHO. HIV. Available from:,2.0%20million%5D%20people%20acquired%20HIV [Accessed December 1st, 2022]

  15. Jahagirdar D. Wrong Code. Available from: [Accessed December 1st, 2022]

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  17. Quinn TC. Global epidemiology of HIV infection. In: Bartlett JA, Bogorodskaya M (eds.). UpToDate. 2022.

  18. Kelley CF, Pollack I, Yacoub R, Zhu Z, Van Doren VE, Gumber S et al. Condomless receptive anal intercourse is associated with markers of mucosal inflammation in a cohort of men who have sex with men in Atlanta, Georgia. Journal of the International AIDS Society. 2021;24(12):e25859. DOI: 10.1002/jia2.25859

  19. Cohen MS. HIV infection: Risk factors and prevention strategies. In: Gulick RM, Mitty J (eds.). UpToDate. 2022.

  20. National AIDS Trust. HIV in the UK statistics. Available from: [Accessed December 1st, 2022]

  21. European Monitoring Centre for Drugs and Drug Addiction. Guidelines for testing HIV, viral hepatitis and other infections in injecting drug users. Luxembourg: Publications Office of the European Union, 2010. Available from: [Accessed December 2nd, 2022]

Please note: the information we provide to you here is for educational purposes only. If you’re experiencing any discomfort or have any complaints or questions about your health, please contact your doctor or other relevant health professional. We don’t provide medical advice.


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