Flu is a contagious respiratory illness caused by the influenza viruses. The virus can cause mild and severe illness, and all degrees in between. The best way to prevent the Flu is to take a flu vaccination each year. Older people, young children, and some people with chronic diseases have a higher risk of getting serious Flu complications.
Key symptoms of the Flu include fever, headache, tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches. Complications include bacterial pneumonia, dehydration, and worsening of certain chronic medical conditions. For more information about Flu and pneumonia, especially vaccination, visit our section on Flu and and Pneumonia.