Causes of influenza

An infected person can release virus when coughing, sneezing, talking, or breathing. Another person may inhale the particles or transfer virus from a surface to the mouth, nose, or eyes. People can spread infection before they realise they are ill and while symptoms are present. Influenza viruses change over time, so protection from an earlier infection may not cover every circulating strain.

Influenza often begins suddenly with fever, chills, headache, cough, fatigue, and feeling generally unwell. Symptoms can overlap with other respiratory infections. Pneumonia is a possible complication, especially when illness is severe or a person has other health risks, but a cough or fever does not by itself prove pneumonia.

Rest, drink enough fluid to avoid dehydration, and limit close contact while fever or strong symptoms continue. Cover coughs and sneezes, wash hands, and improve ventilation around others. Ask a clinician early about testing or antiviral treatment if you are pregnant, have a long-term condition, have a weakened immune system, or become significantly unwell. Follow local advice about returning to work, school, or shared spaces.

Seek urgent help for severe difficulty breathing, chest pain, blue or grey lips, confusion, fainting, severe dehydration, coughing blood, or a marked deterioration after initial improvement. Babies, older adults, pregnant people, and those with chronic illnesses may need earlier assessment when fever, cough, or profound fatigue develops.

Ask whether your symptoms fit influenza or another infection, whether you need testing or antiviral treatment, how to protect vulnerable household members, and which changes should prompt urgent review.