Influenza or flu is a highly contagious disease caused by Influenza Virus. The initial symptoms may look like a common cold but these aggravate quite fast and may become severe within a few days. The most common symptoms include fever, cough, sore throat, body ache, headache, and extreme tiredness. You should not confuse Flu with a Cold. WHO recommends the most effective way to protect against influenza is to get vaccinated every year