Symptoms of flu
The symptoms of flu usually develop within 1 to 3 days of becoming infected. Most people will feel better within a week.
However, you may have a lingering cough and still feel very tired for a further couple of weeks.
Flu can give you any of the following symptoms:
- a sudden fever – a temperature of 38C (100.4F) or above
- a dry, chesty cough
- a headache
- tiredness and weakness
- aching muscles
- limb or joint pain
- diarrhoea or abdominal (tummy) pain
- nausea and vomiting
- a sore throat
- a runny or blocked nose
- loss of appetite
- difficulty sleeping
Is it flu or a cold?
It can sometimes be difficult to tell if you have flu or just a cold, as the symptoms can be quite similar. The main differences are:
- come on quickly
- usually include fever and aching muscles
- make you feel too unwell to continue your usual activities
- come on gradually
- mainly affect your nose and throat
- are fairly mild, so you can still get around and are usually well enough to go to work
When to visit your GP
If you are otherwise fit and healthy, there's usually no need to visit your GP if you have flu-like symptoms.
You should just rest at home until you feel better, while keeping warm, drinking plenty of water and taking painkillers if necessary.
Read more about how to treat flu
Consider visiting your GP if:
- you're 65 years of age or over
- you're pregnant
- you have a long-term medical condition – such as diabetes, heart disease, lung disease, kidney disease or a neurological disease
- you have a weakened immune system – for example, because you're having chemotherapy or have HIV
- you develop chest pain, shortness of breath or difficulty breathing, or start coughing up blood
- your symptoms are getting worse over time or haven't improved after a week
In these situations, you may need extra treatment to prevent or treat complications of flu.
Usually, you can manage flu symptoms yourself at home and there's no need to see a GP. Most people feel better within a week.
You should consider seeing your GP if you're at a higher risk of becoming more seriously ill. This includes people who:
- are 65 or over
- are pregnant
- have a lung, heart, kidney, liver or neurological disease
- have a weakened immune system
- have diabetes
In these cases, your GP may suggest taking antiviral medication.
Managing your symptoms at home
If you're otherwise healthy, you can look after yourself at home by resting, keeping warm and drinking plenty of water to avoid dehydration.
If you're concerned about coronavirus (COVID-19), be mindful of our ibuprofen advice on the coronavius page.
If you feel unwell and have a fever, you can take paracetamol or anti-inflammatory medicines such as ibuprofen to lower your temperature and relieve aches. Children under 16 shouldn't be given aspirin.
Stay off work or school until you're feeling better. For most people, this will take about a week. See your GP if your symptoms get worse or last longer than a week.
Read the page on preventing flu for more information about stopping the infection spreading to others.
In 2009, the National Institute for Health and Care Excellence (NICE) recommended that doctors should consider treating people in the at-risk groups mentioned above with the antiviral medications oseltamivir (Tamiflu) or zanamivir (Relenza) to reduce the risk of complications of flu.
Antivirals work by stopping the flu virus from multiplying in the body. They won't cure flu, but they may help slightly reduce the length of the illness and relieve some of the symptoms.
Recent research has suggested that Tamiflu and Relenza may not be effective at reducing the risk of flu complications and could cause side effects, so not all doctors agree they should be used.
But there is evidence that antivirals can reduce the risk of death in patients hospitalised with flu. In the light of this evidence, Public Health England says it is important that doctors treating severely unwell patients continue to prescribe these drugs where appropriate.
For more information read the NICE guidelines on antivirals to treat influenza.
Antibiotics aren't prescribed for flu as they have no effect on viruses, although they may be prescribed if you develop a complication of flu, such as a bacterial chest infection.
Complications of flu
Complications of flu mostly affect people in high-risk groups, such as the elderly, pregnant women and those who have a long-term medical condition or weakened immune system.
This is why it's important for people in these groups to have the annual flu vaccination and consider seeing their GP if they develop symptoms of flu.
The most common complication of flu is a bacterial chest infection, such as bronchitis. Occasionally, this can become serious and develop into pneumonia.
A course of antibiotics usually cures a chest infection or pneumonia, but it can very occasionally become life-threatening, particularly in the frail and elderly.
Worsening of existing conditions
In some people with long-term health conditions, getting flu can make their condition worse.
For example, people with lung conditions such as asthma or chronic obstructive pulmonary disease (COPD) may find that their symptoms become more severe when they get the flu.
In people with diabetes, flu can affect blood sugar levels, potentially causing hyperglycaemia (high blood sugar) or, in people with type 1 diabetes, diabetic ketoacidosis (a dangerous condition caused by a lack of insulin in the body).
If you have type 1 diabetes or have type 2 diabetes and take insulin, it's a good idea to monitor your blood sugar level more closely while you’re feeling unwell.
If you get flu while you're pregnant, there's a risk that the infection could cause problems with your pregnancy.
Flu may cause you to go into premature labour (before 37 weeks of pregnancy), or it may result in your baby having a low birth weight.
Occasionally, getting flu during pregnancy can result in a miscarriage or stillbirth.
Less common complications of flu include:
- tonsillitis – inflammation of the tonsils
- otitis media – an infection of the middle ear
- sinusitis – inflammation of the lining of the sinuses (small, air-filled cavities behind your cheekbones and forehead)
- febrile seizures (convulsions) – a fit that can happen when a child has a fever
- meningitis – infection in the brain and spinal cord
- encephalitis – inflammation of the brain
There are 3 main ways of preventing flu:
- the flu vaccination
- good hygiene (such as handwashing and cleaning)
- antiviral medication
The flu vaccine
The annual flu vaccine can help reduce your risk of getting flu each year, although it's not 100% effective because it doesn't work against every possible type of flu virus.
With coronavirus (COVID-19) around, it is more important than ever to get the flu vaccine this autumn to protect yourself, others and the NHS.
Who should be vaccinated against flu this year
To reduce your risk of getting flu or spreading it to other people, you should always:
- make sure you wash your hands regularly with soap and warm water
- clean surfaces (such as your keyboard, telephone and door handles) regularly to get rid of germs
- use tissues to cover your mouth and nose when you cough or sneeze
- put used tissues in a bin as soon as possible
Taking the antiviral medicines oseltamivir (Tamiflu) or zanamivir (Relenza) to prevent flu is recommended if all of the following apply:
- there's a lot of flu around
- you're over 65, pregnant, or have a medical condition that puts you at risk of complications of flu, such as diabetes, heart disease, lung disease, kidney disease or a neurological disease
- you've been in contact with someone with a flu-like illness and can start antiviral treatment within 36-48 hours
- you haven't had the flu vaccination
If there's an outbreak of flu in a residential or nursing home – where the flu virus can often spread very quickly – antiviral medication may be offered to people if they've been in contact with someone with confirmed flu.
For more information, read the guidelines from the National Institute for Health and Care Excellence (NICE) on antivirals to prevent influenza.
Post Flu Vaccine Symptoms
“If someone develops fever post vaccination, this should usually resolve within 48 hours. This is a relatively common, expected reaction, and self-isolation and testing for COVID-19 are not required unless COVID is suspected based on other clinical criteria such as cough and/or anosmia.
If fever persists beyond 48 hours or an individual develops other COVID-19 related symptoms, then they should self-isolate and be recommended to have a test for COVID-19. Testing for COVID-19 may also be considered at any time following clinical assessment, or if there are other epidemiological indications such as being a close contact of a case or part of a cluster.”