Overview
Influenza (flu) is a highly contagious respiratory illness caused by influenza A or B viruses. It causes more severe illness than the common cold. Complications including pneumonia, hospitalisation, and death primarily affect the elderly, the very young, pregnant women, and those with underlying health conditions.
How common is it?
Flu infects between 10 to 30% of the UK population in typical winters. Seasonal epidemics cause thousands of deaths and hundreds of thousands of hospital admissions annually.
Causes and risk factors
Influenza viruses spread through respiratory droplets and contaminated surfaces. The virus mutates frequently, which is why immunity from last year's infection or vaccination provides only partial protection each season.
Common risk factors
- Respiratory droplet spread from close contact
- Age extremes (very young and over 65)
- Chronic heart, lung, kidney, or liver disease
- Diabetes
- Pregnancy
- Immunosuppression
- Obesity
Symptoms
- Sudden onset of high fever (38 to 40°C)
- Severe muscle aches and pains
- Headache
- Dry cough
- Sore throat
- Fatigue and exhaustion
- Runny or blocked nose
- Unlike a cold, flu comes on rapidly and the systemic symptoms are much more severe
When to see a doctor
See a doctor for flu symptoms with breathlessness, chest pain, confusion, or collapse. Seek early antiviral treatment within 48 hours if you are at high risk (elderly, pregnant, immunosuppressed, or those with chronic illness).
Diagnosis
Clinical diagnosis in most cases. Rapid influenza diagnostic tests or PCR swabs confirm the virus in hospitalised patients or when antiviral treatment is being considered.
Treatments
Rest, fluids, and antipyretics
Paracetamol or ibuprofen for fever and muscle pain. Adequate fluid intake. Rest until fever has been gone for at least 24 hours.
Antiviral medication (oseltamivir/Tamiflu)
Most effective when started within 48 hours of symptom onset. Reduces severity and duration by about one to two days. Used for high-risk patients and in hospitalised cases.
Hospital care for severe cases
Oxygen, intravenous fluids, and antibiotic treatment for bacterial superinfections. ICU care for respiratory failure.
Self-care and lifestyle
- Stay home until you have been fever-free for 24 hours without antipyretics
- Wash hands frequently and avoid touching your face
- Cover your mouth and nose with a tissue when coughing or sneezing
- Get the flu vaccine every autumn
Prevention
Annual influenza vaccination is the most effective preventive measure and is recommended for all high-risk groups. The vaccine is updated each year to match circulating strains.