Influenza

Key facts

• Influenza, commonly called the flu, is a contagious respiratory infection caused by influenza A or B viruses that spreads rapidly in crowded environments.
• Fever above 38C, chills, muscle aches, headache, and a dry cough typically appear within one to two days of exposure, and fatigue can be severe.
• Antivirals such as oseltamivir work best when started within 48 hours of the first symptoms.
• Seek prompt medical attention for difficulty breathing, chest pain, persistent high fever, confusion, or cyanosis.

Symptoms and when they strike

Flu tends to arrive abruptly. Fever above 38C, chills, muscle aches, headache, and a dry cough typically appear within one to two days of exposure. Fatigue can be severe enough to keep people in bed for several days. Sore throat and a runny nose are common; vomiting and diarrhoea occur more often in children. Most otherwise healthy adults recover fully within one to two weeks.

Seek medical attention promptly if symptoms include difficulty breathing, chest pain, persistent high fever, confusion, or cyanosis: these can signal serious complications such as pneumonia. Older adults, young children, pregnant women, and people with existing heart, lung, or immune conditions face a higher risk of complications and should have a lower threshold for seeking care.

Antiviral treatment

Antivirals work best when started early, ideally within 48 hours of the first symptoms. Oseltamivir (Tamiflu) is the most widely used option; it reduces the duration and severity of illness by inhibiting the neuraminidase enzyme that allows the virus to spread between cells. Rest, adequate fluids, and paracetamol or ibuprofen for fever and pain support recovery alongside antiviral therapy. An annual flu vaccine remains the most effective way to lower the chance of catching influenza in the first place, and it also tends to reduce the severity of illness in people who catch it anyway.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.