Influenza, also known as "the flu", is a viral infection caused by the influenza virus, and is characterized by a sudden onset of high fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and runny nose.
Cough can be severe and can last 2 or more weeks. Most people recover from fever and other symptoms within a week without requiring medical attention.
But influenza can cause severe illness or death especially in people at high risk. The time from infection to illness, known as the incubation period, is about 2 days.