Influenza is an acute viral infection caused by influenza type A or B virus (less commonly C). It is characterized by sudden onset, high fever, muscle pain, headache, cough.
Influenza is dangerous with complications, especially for the elderly and people with chronic diseases. Influenza is easily transmitted by airborne droplets, and the greatest contagiousness usually occurs in the first days of illness. An important prevention is an annual vaccination, which reduces the risk of severe disease and complications.