After infection, it takes 1-3 days for symptoms to develop. Healthy people mostly have symptoms of a sore throat, dry cough, nausea and sore eyes. Fever, chills, muscle aches and pains, loss of appetite occur in more severe cases. These symptoms usually settle after a week. You often feel very tired for days or even weeks after the flu.
Some people can have life threatening complications.
Influenza can be severe or even fatal if a person is not in good health to begin with. The body and its defences can also become so weakened by influenza that other infections can occur. Pneumonia, sinusitis, airway or inner ear infection may occur. Rare and sometimes fatal problems include inflammation of the brain and nervous system and kidneys. Influenza can also worsen other problems such as diabetes, chronic bronchitis or heart failure.