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Influenza (Flu)
What is Influenza (Flu)
Influenza (Flu) is a common viral illness that affects the nose, throat, and lungs. It is easily transmitted, especially during autumn and winter months. It can cause symptoms such as fever, cough, sore throat, muscle pain, and fatigue. While most individuals recover within a week, tiredness may persist for a while.
Certain groups are more likely to get critically ill, such as elderly individuals, small children, pregnant women, and individuals with specific long-term health problems. This guide explains what Flu is, how it spreads, its symptoms, management options, and when to seek medical advice.
Quick facts
- Caused by influenza viruses.
- Mostly affects the nose, throat, and lungs.
- Most people recover within a week, though fatigue may continue longer.
- Coughs, sneezes, and close contact all contribute to its rapid spread.
Disclaimer: This content is for general informational and educational purposes only. It is not intended to replace professional medical advice, diagnosis or treatment. Always seek advice from a qualified healthcare professional regarding any medical concerns. In an emergency, call 999 or go to your nearest A&E department.
This content is medically reviewed by Dr Karthik Baskaran. Last updated: 15 October 2026.
Type of influenza virus
Influenza A
Influenza A is the most prevalent flu virus. It is one of the main causes of seasonal Flu in the UK each winter. It infects humans and animals, including birds and pigs, and is the only influenza type linked to pandemics.
Influenza B
Influenza B also circulates every flu season and causes similar symptoms. It mainly infects humans, tends to cause less severe outbreaks, has not caused flu pandemics and is included in the seasonal flu vaccine. While it can still cause serious disease, it normally progresses more slowly than Influenza A.
Influenza C
Influenza C is less common than influenza A and B and usually causes mild respiratory symptoms. It is rarely associated with serious outbreaks and is not included in the seasonal flu vaccine.
Influenza D
Influenza D primarily affects cattle and other livestock rather than humans. It is not included in human flu vaccines, but researchers continue to monitor it closely.
Symptoms of Flu
Warning: If you experience significant breathing difficulties, chest discomfort, disorientation, or signs of extreme dehydration, get immediate medical attention.
Causes of Flu
Flu is caused by influenza viruses that are easily transmitted from person to person, especially during the colder months.
Influenza viruses: Flu is caused by influenza viruses, most commonly types A and B, which infect the cells lining your nose, throat, and airways.
Seasonal patterns: Flu circulates every year, with cases usually peaking between December and March in the UK. The virus changes over time, so the flu vaccine is reviewed and updated each year.
Winter months: Cold weather encourages people to stay indoors in close contact with others, making it easier for the flu virus to spread.
Exposure risks: Being in busy locations, living with someone who has the Flu, or having close contact with an infected person increases your chances of catching the virus.
Flu Management
Most people recover at home with rest and supportive care.
| Recommendation | Why it helps |
|---|---|
| Rest | Helps your body fight the infection. |
| Drink plenty of fluids | It helps prevent dehydration. |
| Take doctor-prescribed medicine (if clinically appropriate) | It helps reduce fever and relieve aches. |
| Eat light, nutritious meals | It supports recovery. |
This information is for educational purposes only. You should consult a doctor or medical practitioner before attempting home remedies to ensure they are safe for your specific condition.
How Hola Health UK may help
- Discuss your symptoms: Explain your symptoms, when they started and how they are affecting your daily activities.
- Receive medical advice: A doctor can assess your symptoms and offer advice on managing flu, where clinically appropriate.
- Understand your care options: Your doctor can advise you on the next steps, including whether you need an in-person assessment or further medical care.
- Request a sick note: If flu symptoms affect your ability to work or study, you can discuss your situation with a doctor. A sick note may be issued if clinically appropriate.
Hola Health UK offers private online consultations every day from 8 am to 6 pm. We’re a private service, not an NHS provider. An online consultation may not be suitable if you need an urgent examination or immediate medical attention.
If you experience severe difficulty breathing, sudden chest pain or other signs of a medical emergency, call 999.
FAQ
How the Flu Spreads
The Flu spreads easily from person to person, especially in enclosed spaces during the winter months. Understanding how it spreads can help you protect yourself and those around you.
- Airborne droplets: When someone with the flu coughs, sneezes, or speaks, they release tiny droplets containing the virus into the air. People nearby may breathe them in and become infected.
- Close contact: You can contract the Flu through close contact with an infected individual, such as handshakes, hugging, or touching a surface that an infected person has recently touched and then touching your face.
- Contaminated surfaces: Flu germs from coughs and sneezes can survive on hands and hard surfaces such as door knobs, phones, and worktops for up to 24 hours. Touching these surfaces and then touching your face might transmit the virus.
How Long Is Influenza Contagious?
Most people can spread the Flu from approximately one day before symptoms appear to five to seven days after being ill. Young children and people with compromised immune systems may be contagious for longer.
What are the symptoms of flu in Children & Older adults
Symptoms in Children
| Symptom area | What to look out for |
|---|---|
| General | Sudden high temperature, tiredness, and appearing less active than usual. |
| Ears and eyes | Earache and sore eyes. |
| Glands | Swollen glands in the neck. |
| Digestive | Tummy pain, diarrhoea, feeling or being sick (more common in children than adults). |
| Behaviour | Being unusually clingy, irritable, and difficult to console. |
| Vomiting | May occur, especially in younger children. |
Symptoms in Older Adults
- Fever might be low or absent.
- Confusion may be an early indicator.
- Weakness and disorientation might become more obvious.
- Existing medical issues may worsen.
- Recovery time is often lengthier in older people.
Who Is More Likely to Get the Flu?
Some people are more likely to contract the flu or experience problems.
- Children: Children’s immune systems are still developing; therefore, diseases spread rapidly in schools and nurseries.
- Pregnant women: Pregnancy alters the immune system, raising the risk of serious disease.
- Older adults: As we age, our immune systems weaken, making recovery more challenging.
What are the risk factors for Severe Flu
Some individuals are at a higher risk of becoming seriously ill if they catch the Flu. This is often because their immune system or overall health makes it difficult to fight the infection.
- Age 65 or over – the immune system naturally weakens with age.
- Pregnancy – the body’s response to infection changes during pregnancy.
- Long-term conditions – such as asthma, heart disease, diabetes, or kidney or liver disease.
- Weakened immune system – for example, due to chemotherapy, HIV, or certain medicines.
- Being overweight – a BMI of 40 or above is associated with a higher risk of complications.
- Living in a care home – close contact with others can increase both exposure and risk.
Warning: People with these risk factors should seek medical attention right away if they have flu symptoms to discuss assessment and whether antiviral treatment is appropriate.
How Is the Flu Diagnosed?
The majority of cases are identified using your symptoms and medical history.
- Symptom assessment: A doctor or medical practitioner can usually identify the flu based on your symptoms and the speed at which they developed, especially during the flu season.
- Swab test: A nose or throat swab can confirm whether you have the Flu and, when needed, help distinguish it from COVID-19 or other infections.
- Further assessment: If you’re in a higher-risk group or have severe symptoms, additional checks, such as listening to your chest, may be required.
Physical examinations (such as listening to the chest) cannot be performed via telehealth and may be required for those in high-risk groups.
How Long Does Flu Last?
| Time | What to expect |
|---|---|
| Days 1–3 | Fever, aches and cough begin suddenly. |
| Days 4–7 | Symptoms gradually improve. |
| 1–2 weeks | Most people recover. |
| 2+ weeks | Fatigue or cough may continue. |
What are the possible complications of flu?
Although most individuals recover without a problem, the Flu can occasionally cause complications, particularly in those at higher risk.
- Chest infections, including pneumonia — the Flu can make it easier for a bacterial infection to take hold in the lungs.
- Worsening of long-term conditions such as asthma or COPD, heart disease or diabetes.
- Ear infections are more common in children than in adults.
- Dehydration can happen if fluid intake is low while you’re unwell.
- Hospital admission may be needed in more serious cases, especially among older adults, young children, and pregnant women.
What are the stages of Flu
Stage 1 – Exposure This is the stage where you come into contact with the flu virus, often through droplets released by coughing or sneezing or by touching contaminated surfaces. Expected duration: a single moment of contact.
Stage 2 – Incubation During this stage, the virus begins to multiply in your body without causing noticeable symptoms. However, you can still spread the infection to others during this time. Expected duration: Around one to four days.
Stage 3 – Symptom Onset and Peak Flu symptoms usually come on suddenly and can include a high fever, aching body, tiredness, and a dry cough. Most people feel the worst during the first two or three days of illness. Expected duration: Around three to five days.
Stage 4 – Recovery Most symptoms gradually improve, although a cough and tiredness may last for a week or two after the main symptoms have settled. Expected duration: Around one to two weeks.