Overview
Flu, short for influenza, is an infection of the nose, throat and lungs caused by influenza viruses. Two types cause seasonal illness in people, influenza A and influenza B.
The viruses change slightly from year to year, which is why flu comes back in waves and why the is updated and given every year. The time between catching the virus and falling ill is short, usually about two days.
Most people recover within a week without any specific treatment. For some, particularly the very young, older people, pregnant women and anyone with a long-term illness, flu can become serious.
Symptoms
Flu usually arrives suddenly, over a few hours rather than a few days:
- Fever and chills
- Aching muscles and joints
- Headache
- A dry cough
- Sore throat and a runny or blocked nose
- Exhaustion, and often difficulty sleeping
- Loss of appetite
The difference from a common cold is the speed and the reach. A cold builds up gradually and stays mainly in the nose and throat, while flu affects the whole body and usually stops someone carrying on as normal. The cough and the tiredness can drag on for a couple of weeks after the fever has gone.
When to see a doctor
Speak to a doctor sooner rather than later if you are pregnant, over 65, have a long-term condition such as asthma, diabetes or heart, lung, liver or kidney disease, or have weakened immunity. Also seek advice if symptoms have not improved after seven days, if they are getting worse, or if you are short of breath.
Causes
Flu spreads mainly in the tiny droplets released when someone with flu coughs, sneezes or talks, and these are breathed in by people nearby. The virus can also survive for a time on hands and on surfaces such as door handles, and reaches the body when someone touches their eyes, nose or mouth.
A person can pass the virus on from shortly before symptoms appear and for several days afterwards, which is why staying at home while unwell protects other people.
Risk factors
- Age over 65
- Children under five, and especially under two
- Pregnancy
- Long-term conditions such as asthma and other lung disease, heart disease, diabetes, kidney or liver disease
- A weakened immune system, for example from cancer treatment, long-term steroids or HIV
- Health and care work, and crowded indoor settings
Complications
The commonest serious complication is pneumonia, an infection deep in the lungs, which can be caused by the flu virus itself or by bacteria that take hold afterwards. Severe infection can go on to affect the whole body.
Flu also brings on ear and sinus infections, and it frequently makes existing conditions worse: asthma attacks, poorer control of diabetes, and strain on a weakened heart.
Prevention
- A flu every year, particularly for older people, pregnant women, young children, health workers and anyone with a long-term illness
- Washing hands with soap and water regularly
- Covering the mouth and nose with a tissue or the bend of the elbow when coughing or sneezing
- Staying at home while unwell, and away from people at higher risk
- Keeping rooms ventilated
- Not touching the eyes, nose and mouth with unwashed hands
Diagnosis
Flu is usually recognised from the symptoms and the time of year, and most people do not need a test. A swab from the nose or throat can confirm the virus where it matters, for example in someone who is in hospital, who is at high risk, or where an outbreak is being investigated.
A chest X-ray or blood tests may be done if pneumonia or another complication is suspected, or if the fever points to something other than flu.
Treatment
Most people manage flu at home. Rest, plenty of fluids, and paracetamol for fever and aches are the mainstay. Check the label of any combined cold and flu remedy, because many already contain paracetamol and taking both together is unsafe. Aspirin should not be given to children and young people under 16.
Antiviral medicines are available and can shorten the illness. They work best when started early, so they are usually offered to people at higher risk of serious illness rather than to everyone.
do not treat flu itself and are added only when a bacterial infection, such as pneumonia or an ear infection, develops on top of it. Anyone who is struggling to breathe, or who is very drowsy, is assessed in hospital.
Myths and facts
Things people often say about this. Open each one to see what is true.
Myth“The flu vaccine gives you flu.”What is true?
Fact
It cannot. The CDC states plainly that flu vaccines cannot cause flu illness, because the injected vaccines are made with killed virus or with a single protein from the virus. A sore arm or a day of feeling a bit off is a normal reaction, not the illness itself.
Myth“Flu is just a bad cold.”What is true?
Fact
Flu tends to be more severe than a cold and affects more than the nose and throat, often leaving someone too unwell to carry on as normal. It can lead to pneumonia and other serious problems, particularly in the very young, older people, pregnant women and anyone with a long-term illness.
Myth“Antibiotics will clear the flu faster.”What is true?
Fact
Antibiotics do not work on viruses, and flu is caused by a virus. They are prescribed only if a bacterial infection such as a chest or ear infection develops on top of the flu. Taking them unnecessarily causes side effects and adds to antibiotic resistance.
Myth“Only elderly people need to bother about flu.”What is true?
Fact
Older people are at higher risk, but so are pregnant women, children under five and especially under two, and anyone with asthma, diabetes, heart disease or weakened immunity. Health workers are also more exposed. These are exactly the groups for whom a yearly vaccine is advised.
Myth“You catch flu from getting cold, wet or sitting in a draught.”What is true?
Fact
Flu is caused by influenza viruses, which pass between people in the droplets from coughs, sneezes and talking, and can survive for a while on hands and surfaces. Getting chilled does not create the virus. Washing hands and covering coughs are what interrupt it.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
Do I need the flu vaccine every year?
Yes, for two reasons. The influenza viruses change from season to season, so the vaccine is updated to match them, and the protection from a previous dose fades over time. An annual dose is what keeps the protection current.
How long should I stay away from work or school?
Stay at home while you have a fever and while you feel unwell, and give yourself time before going back, especially if you work near people at higher risk. Flu can be passed on from shortly before symptoms start and for several days after, so hand washing and covering coughs still matter once you return.
The fever has gone but the cough will not stop. Is that a problem?
A dry cough and tiredness often linger for a week or two after flu, and that on its own is not worrying. Go back to the doctor if the cough comes with fresh fever, breathlessness or chest pain, or if you start bringing up blood.
