Flu (Influenza)
How to tell flu from a cold, how to look after yourself, who needs to take extra care, and what the vaccine can and cannot do.
Flu is often used as a catch all word for any bad cold, but true influenza is a different and usually much more unpleasant illness. Most healthy people recover fully with rest at home. For some people it can be serious, which is why it helps to know who is at higher risk and which warning signs matter.
What is flu?
Flu is an infection of the nose, throat, and lungs caused by influenza viruses. In the UK it circulates mainly between December and March. It spreads through droplets from coughs and sneezes, and from hands and surfaces contaminated with the virus.
Typical symptoms
A sudden high temperature, aching muscles, exhaustion, a dry cough, headache, sore throat, and loss of appetite. Children may also have tummy pain, diarrhoea, or earache.
How infectious it is
You can pass flu on from around a day before symptoms begin and are most infectious in the first three to five days of illness. Children and people with weakened immunity can be infectious for longer.
Flu or a cold?
A useful rule of thumb is that with a cold you feel unwell but can usually get on with things, while flu tends to put you in bed.
| Flu | Cold | |
|---|---|---|
| Onset | Sudden, often within a few hours | Gradual, over a day or two |
| Fever | Common, often 38°C or above | Uncommon or mild |
| Aches and pains | Common and often severe | Mild if present |
| Exhaustion | Marked, often confining you to bed | Mild, you can usually carry on |
| Runny or blocked nose | Sometimes | The main symptom |
| Cough | Usually dry and can be severe | Mild to moderate |
COVID and other winter viruses can cause very similar symptoms, and it is often impossible to tell them apart without a test. For most people the self care advice is the same.
How long it lasts
Symptoms usually peak over the first two to three days and most people start to feel better within about a week. A cough and tiredness can linger for two to three weeks, which is normal and does not usually mean something has gone wrong.
What matters more is the direction of travel. Starting to improve and then becoming worse again, with a returning fever, new breathlessness, or chest pain, can be a sign of a secondary chest infection and should be assessed.
Looking after yourself
There is no cure for flu. Treatment is about staying comfortable while your immune system clears the virus.
What helps:
- Rest and sleep, and stay off work or school until you feel well enough to return
- Drink plenty of fluids, aiming for pale yellow urine
- Take paracetamol or ibuprofen for fever and aches, following the packet instructions
- Keep warm, and eat what you can manage
- Stay at home and avoid contact with vulnerable people while you have a fever
- Catch coughs and sneezes in a tissue, bin it, and wash your hands
Check the label on cold and flu remedies. Many contain paracetamol, so taking them alongside paracetamol tablets can lead to an accidental overdose. Ibuprofen is not suitable for everyone, including some people with asthma, kidney problems, or stomach ulcers, and should be avoided in pregnancy. Do not give aspirin to children under 16.
Who is at higher risk?
Some people are more likely to develop complications such as pneumonia. If you are in one of these groups and think you have flu, contact a doctor early rather than waiting to see how it goes.
Age
Adults aged 65 and over, and babies and young children, particularly those under two.
Pregnancy
Pregnant women at any stage, and for two weeks after giving birth.
Long term conditions
Chronic heart, lung, kidney, liver, or neurological disease, diabetes, and asthma requiring regular preventer treatment.
Weakened immunity
From conditions such as HIV, treatments such as chemotherapy or long term steroids, or having no working spleen.
Severe obesity
A BMI of 40 or above is associated with a higher risk of severe illness.
Care settings
People living in residential or nursing homes, where flu can spread quickly.
Antivirals & antibiotics
Antivirals
Antiviral medicines such as oseltamivir can shorten the illness by around a day and may reduce the risk of complications. They work best when started within 48 hours of symptoms beginning. They are generally reserved for people in higher risk groups or with severe illness, and are not usually needed by otherwise healthy adults.
Antibiotics
Antibiotics do not work against viruses, so they will not treat flu or speed up recovery. They are only used if a bacterial complication develops, such as pneumonia. Taking them when they are not needed exposes you to side effects and contributes to antibiotic resistance.
The flu vaccine
Vaccination is the most effective way to reduce your risk of flu and its complications. The NHS offers it free each year to people at higher risk, including those aged 65 and over, pregnant women, people with certain long term conditions, carers, and children. Eligibility is reviewed annually, so check current NHS guidance. Anyone else can choose to have it privately.
The vaccine cannot give you flu
The injected vaccine contains no live virus. Some people have a sore arm, mild aches, or a slight temperature for a day or two, which is the immune system responding, not flu itself.
You need it every year
Flu viruses change constantly and protection fades over time, so the vaccine is updated each year to match the strains expected to circulate.
It takes about two weeks to work
Protection builds over 10 to 14 days. Autumn is the ideal time to be vaccinated, before flu starts circulating widely.
It is not perfect, but it helps
Effectiveness varies from year to year depending on how well the vaccine matches circulating strains. Even in a poorer match year, vaccinated people who catch flu tend to have milder illness.
Tell the person vaccinating you if you have had a serious allergic reaction to a previous flu vaccine or have a severe egg allergy. If you are unwell with a fever on the day, it is usually best to wait until you have recovered.
When to get help
Call 999 or go to A&E if you or someone you are caring for:
- Is struggling to breathe or is too breathless to speak in full sentences
- Has sudden chest pain
- Is coughing up blood
- Is confused, very drowsy, or difficult to wake
- Has blue or grey lips, or pale, blotchy, cold skin
- Has a rash that does not fade when a glass is pressed against it
Contact us or NHS 111 if:
- You are in a higher risk group and think you have flu
- Your symptoms have not improved after seven days
- You started to get better and then became worse again
- You cannot keep fluids down or are passing very little urine
- You are worried about a baby or young child
Common questions
Short answers to the questions we are asked most often.
How can I tell if I have flu or a cold?
Flu comes on suddenly, often within a few hours, with a high temperature, aching muscles, and exhaustion that usually puts you in bed. A cold comes on gradually over a day or two, mainly affects the nose and throat, and you can usually carry on with normal activities.
How long does flu last?
Symptoms usually peak over the first two to three days and most people start to feel better within about a week. A cough and tiredness can linger for two to three weeks. Getting better and then worse again should be assessed by a doctor.
Do antibiotics help with flu?
No. Flu is caused by a virus and antibiotics do not work against viruses. They are only used if a bacterial complication such as pneumonia develops. Antiviral medicines may be offered to people at higher risk and work best when started within 48 hours of symptoms beginning.
Can the flu vaccine give you flu?
No. The injected flu vaccine contains no live virus, so it cannot cause flu. Some people have a sore arm, mild aches, or a slight temperature for a day or two, which is the immune system responding. Protection takes around 10 to 14 days to build.
When should I get urgent help for flu?
Call 999 or go to A&E for difficulty breathing, sudden chest pain, coughing up blood, confusion or severe drowsiness, blue or grey lips, or a rash that does not fade under a glass. Contact a doctor or NHS 111 if you are in a higher risk group or are not improving after seven days.
Next steps
If you are unwell and would like to speak to a doctor, or would like to ask about vaccination, please get in touch. If you have a fever or cough, let us know when you book so we can arrange the most appropriate type of appointment.