HIV (human immunodeficiency virus) is a virus that attacks the body’s immune system. Without treatment, it can lead to Aids (acquired immunodeficiency syndrome). Once people get HIV, they have it for life.
HIV targets the body’s white blood cells, weakening the immune system. This makes it easier to get sick with diseases like tuberculosis, infections and some cancers. HIV is spread from the body fluids of an infected person, including blood, breast milk, semen and vaginal fluids. It is not spread by kisses, hugs or sharing food. It can also spread from a mother to her baby.
Signs and symptoms vary depending on the stage of infection with the majority of people unaware they are infected until the later stages of the disease. Some people may experience flu-like symptoms within two to four weeks after infection, which may last for a few days or several weeks. Some people have no symptoms at all. The symptoms of HIV vary depending on the stage of infection.
Other signs and symptoms include:
Without treatment, people living with HIV infection can also develop severe illnesses such as tuberculosis (TB), cryptococcal meningitis, severe bacterial infections, and cancers such as lymphomas and Kaposi’s sarcoma. HIV exacerbates other infections, such as hepatitis C, hepatitis B and mpox.
When people with HIV do not get treatment, the disease typically progresses through three stages. Without treatment, people with Aids typically survive about three years.
Stage one – acute HIV infection – develops within two to four weeks and people may have flu-like symptoms. There is a high level of HIV in the blood, greatly increasing the risk of transmission.
In stage two – chronic HIV infection – HIV is still active and continues to reproduce in the body. People may not have any symptoms or get sick during this phase but can transmit HIV. Without treatment, this stage may last a decade or longer, or may progress faster.
Stage three – Aids – is the end-stage of HIV infection if left untreated, when severe damage to the immune system occurs. The body cannot fight off infections and sufferers can transmit the disease easily to others. However, even at this stage therapy can still be effective.
Most people get HIV through anal or vaginal sex, sharing needles, syringes, or other drug injection equipment. HIV can also be transmitted from the mother to the child via breast milk or during pregnancy.
People do not spread HIV through ordinary day-to-day contact such as kissing, hugging, shaking hands or sharing food or water.
There is no cure for HIV infection, however drugs are now so effective that the disease is no longer a death sentence and people with the virus can go on to lead long and healthy lives. HIV is treated with antiretroviral drugs (ART), which stop the virus from replicating in the body. ART reduces the amount of HIV in the blood – viral load – to such a low level that it is undetectable. Those with an undetectable viral load cannot transmit HIV to others.
There are many different types of HIV drugs in different formulations – from daily pills to injections taken every other month. Long acting injectables – administered every six months – are also in development.
Prevention strategies include: using condoms the right way every time you have sex, and never sharing needles, syringes, or other drug injection equipment.
Pre-exposure prophylaxis – PrEP – is a combination of pills that can be taken by anyone at risk of HIV – for example, your partner has HIV, you regularly have sex with people without using a condom or you inject drugs. After a long campaign PrEP is now available on the NHS. In 2025 the US Food and Drug Administration approved the anti-viral lenacapavir, a single shot of which provides protection for six months.
Post-exposure prophylaxis – PEP – is also available in an emergency when you think you have been exposed to an HIV infection, for example a condom has split or you are a health worker.
People living with HIV can prevent passing the virus to others by taking their medication and getting regularly tested.
The disease is thought to have originated in Leopoldville – the capital of the Belgian colony of the Congo – when the virus crossed from monkeys into humans at the turn of the 20th century. But it exploded into the public consciousness in the 1980s with the first reports of the disease among gay men and people with haemophilia in the west.
The first ART drug was approved for use in the US in 1987 but there were still high profile deaths – such as that of Freddie Mercury in 1991. This led to campaigning by celebrities such as Elton John who donated money for treatment and research.
The 1990s saw a host of scientific breakthroughs including the first trial of an HIV vaccine – although that still remains elusive – and improved ARTs. However, despite the huge progress HIV remains a major global public health issue, having claimed an estimated 44.1 million lives by the end of 2024. Transmission is ongoing in all countries globally. There were an estimated 40.8 million people living with HIV at the end of 2024, two thirds of whom live in Africa. In the same year, an estimated 1.3 million people acquired HIV.
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