What should you know about different types of influenza?

Influenza A and B are the main types that commonly cause seasonal illness in people. Influenza A has subtypes based on proteins on its surface and can infect animals as well as people. Influenza B is grouped into lineages rather than the same subtype system. Influenza C usually causes a milder illness, while influenza D mainly affects cattle.

The illness often begins abruptly with fever, chills, headache, cough, fatigue and a general feeling of being unwell. Symptoms can overlap with other respiratory infections, and influenza can sometimes lead to pneumonia.

Rest, drink fluids and stay home while fever or marked symptoms continue. Reduce close contact, improve ventilation and cover coughs. A clinician may consider antiviral treatment when illness is severe or the person has a higher risk of complications; this works best when started early. Antibiotics do not treat influenza itself.

Follow local vaccination advice, especially if you are pregnant, older, or have a long-term medical condition. Ask a clinician which preventive steps fit your circumstances.

Seek emergency care for severe breathing difficulty, chest pain, blue lips, confusion, fainting, dehydration or symptoms that improve and then suddenly worsen. A persistent or worsening cough with breathlessness can signal pneumonia or another complication.

Ask whether testing is useful, whether antiviral treatment is suitable, when you can return to normal activities, and which warning signs should prompt urgent review.