Influenza (flu) and HIV

Mareike Günsche |

Key points

  • People living with HIV are recommended to have the flu vaccine every year.
  • Flu is very contagious and spreads in the same way as colds.
  • You can get flu at any time of the year, but it is more common in winter.

Influenza, usually known as the flu, is a very common viral illness that affects the respiratory tract.

The flu is different to the common cold. Colds and flu share some of the same symptoms but flu symptoms tend to be more severe and last longer.

You can get flu at any time of the year, but it is more common during the winter season. Because of this, it is sometimes referred to as seasonal flu. In the UK, a flu vaccination programme is provided by the NHS each year that runs during the autumn (see below for more information).

People living with HIV are urged to have their flu vaccine each year. You may be offered a flu vaccine and a COVID-19 vaccine at the same time. 

How is flu spread?

Flu is very contagious and spreads from one person to another in tiny droplets when someone with flu coughs or sneezes – the same way colds and COVID-19 are spread. The virus sits in the air before falling down to surfaces where it can live for up to 24 hours. People can be infected by breathing in the droplets directly from the air or by touching objects that have the virus on them, such as phones, keyboards and door handles.

The incubation period for flu (the time between catching an infection and symptoms appearing) is normally around one to three days. People are usually most infectious from the day they develop symptoms and for a further three to seven days, and are not considered infectious anymore once their symptoms have disappeared. People with weakened immune systems and children may stay infectious for longer.

What are the symptoms of flu?

Flu symptoms tend to develop quite suddenly and are often at their worst two or three days after infection. They usually start to improve after about a week but it may take longer to feel completely better.

Flu symptoms can include:

  • fever or high temperature (over 38°C or 100.4°F)
  • headache
  • tiredness and weakness
  • chills
  • a runny or blocked nose
  • sneezing
  • sore throat
  • a dry, chesty cough
  • aching muscles and limb or joint pain
  • difficulty sleeping
  • loss of appetite
  • diarrhoea and abdominal pain
  • nausea and vomiting.

You should contact your GP if you develop chest pain, difficulty breathing, or start coughing up blood; if your condition is still getting worse after seven days; or if a child under 12 months shows symptoms of flu.

Flu can, in some cases, lead to complications and more serious illness (such as bronchitis or pneumonia) and can make some long-term health conditions worse. People at higher risk of this should consider contacting their GP if they have flu symptoms. These are:

  • pregnant women
  • people aged 65 and over
  • people with long-term medical conditions - including HIV - as well as respiratory diseases like asthma or tuberculosis (TB), diabetes, kidney disease, lung disease, heart disease or a neurological disease
  • people with a weakened immune system, such as people with a low CD4 cell count or those having chemotherapy.

Treating flu

Generally, you should stay at home, rest, drink plenty of fluids, keep warm, and use over-the-counter painkillers (such as paracetamol or ibuprofen) to relieve symptoms.



A substance that contains antigenic components from an infectious organism. By stimulating an immune response (but not disease), it protects against subsequent infection by that organism, or may direct an immune response against an established infection or cancer.



Any perceptible, subjective change in the body or its functions that signals the presence of a disease or condition, as reported by the patient.



How well something works (in real life conditions). See also 'efficacy'.

CD4 cell count

A test that measures the number of CD4 cells in the blood, thus reflecting the state of the immune system. The CD4 cell count of a person who does not have HIV can be anything between 500 and 1500. When the CD4 count of an adult falls below 200, there is a high risk of opportunistic infections and serious illnesses.


A drug that acts against a virus or viruses.

If you are in the higher risk groups, your GP may suggest that you take one of the antiviral medications that are used to treat flu – oseltamavir (Tamiflu) or zanamivir (Relenza). The drugs must be taken at or near the start of the illness to be effective. They are not a cure, but can relieve symptoms and shorten the length of time you are ill.

Not all doctors agree that antivirals should be prescribed as research has suggested that they may not be effective at reducing the risk of complications of flu and they may cause side-effects. However, evidence shows that people who are seriously unwell, or who are at risk of becoming seriously unwell, should be prescribed these drugs.

If you take antiviral drugs but your condition does not improve, contact your GP.

As flu is viral, not bacterial, antibiotics will not work. However, if you develop a complication of flu, such as a bacterial chest infection, they may be prescribed.

Preventing flu

Good hygiene is the most effective way of stopping the transmission of viruses such as flu viruses. Washing your hands regularly with soap and water and cleaning surfaces regularly will help prevent infection. For people with flu, sneezing and coughing into a tissue, throwing the tissue away and then washing your hands, will also help prevent onward transmission.

Flu can be prevented (as well as treated) with the antiviral medicines oseltamavir (Tamiflu) and zanamivir (Relenza). In some situations, people living with HIV may be prescribed these as a preventive measure.

Having a low CD4 cell count can increase the risk of complications of flu (and having a condition such as asthma or TB as well can increase the risk further). If you do have a low CD4 count or an AIDS-defining illness, it would be a good idea to check with your HIV clinic whether you could be taking any other action to reduce your risk of getting flu. However, the most useful action you can take is to have an annual flu vaccination.

The flu vaccine

Vaccines against flu viruses are available. Because there are different types of flu viruses, and different strains within those types, with strains changing and new strains emerging over time, the make-up of the vaccine is reviewed each year to include the most prevalent strains.

It is recommended that people in higher risk groups, including people living with HIV of all ages, have the vaccination every year.

Household members and other close contacts of people who are immunocompromised (have a weakened immune system) should also have the flu vaccine. People living with HIV who have a CD4 count below 200 would be considered to be immunocompromised.

The vaccine is also available for people aged 65 and over, pregnant women, people with other long-term health conditions, health workers, carers, and children aged 2-16 years.

In the UK, vaccination is free of charge for people in these groups.

"Good hygiene is the most effective way of stopping the transmission of viruses such as flu viruses."

The vaccine only provides protection for about a year, so it is important you are revaccinated each year.The best time to have the vaccine is in the autumn, between September and early November.

The vaccine is available at GP surgeries. You will need to be registered with a GP and to have told them of your HIV status to be eligible. If you have a low CD4 cell count, anyone you live with may also be eligible for free vaccination. Ask your GP about this. You can also talk to your GP about having vaccinations against COVID-19 and pneumococcal disease.

The seasonal flu vaccine that most adults take doesn’t have ‘live’ virus in it, so it is safe for use by people living with HIV. The vaccine is effective for people living with HIV, although there is some evidence that people with low CD4 counts are less likely to be protected by it (however, it may reduce the risk of complications).

Pregnant women living with HIV can have the flu vaccine.

Your GP should take into account other drugs you are taking that may interact with the flu vaccine. The HIV Pharmacy Association (HIVPA) advises that there are no interactions between the flu vaccine and antiretrovirals (anti-HIV drugs). Therefore, it is safe to take antiretrovirals with the flu vaccine and the vaccine is recommended for people living with HIV.

There is more information on flu vaccination on the NHS website.

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