Stages of Influenza

Flu follows a fairly predictable course. Knowing the stage helps you recognise when to rest and when to seek help.

1. Incubation (1 to 4 days)

The virus multiplies. You may feel well, but you can start to spread it about a day before symptoms.

2. Sudden onset (days 1 to 3)

Fever, chills, body ache, headache, sore throat and extreme tiredness. This is the most contagious and most uncomfortable period.

3. Peak illness (days 3 to 5)

Fever, cough and weakness are at their worst. Fluids and rest matter most. High-risk people should be in contact with a doctor.

4. Recovery (days 5 to 7)

Fever settles, and the body ache eases. A dry cough and tiredness may continue.

5. Lingering symptoms (1 to 2 weeks or more)

Cough and fatigue take time to clear. Return to normal activity gradually.

When a stage goes wrong

If the fever returns after improving, or breathing becomes difficult, bacterial pneumonia or another complication may have developed. Seek care.

Contagious period

Most adults can spread flu for about 5 to 7 days from onset. Children and people with weak immunity may spread it longer.

Key point

Early rest and fluids help most. Watch for the signs that mean the illness is becoming serious.

Before your appointment

Note when symptoms began, your highest temperature, and any cough, breathing trouble or vomiting. List your medicines, long-term conditions, pregnancy, allergies and recent vaccines, including this year's flu vaccine. Mention contact with anyone who is ill. Ask about testing, antivirals, when to return to work or school and the warning signs that mean you should call 112 or 102.