Introduction

Influenza is caused by a virus that attacks mainly the upper respiratory tract – the nose, throat and bronchi and rarely also the lungs. The infection usually lasts for about a week. It is characterized by sudden onset of high fever, myalgia, headache and severe malaise, non-productive cough, sore throat, and rhinitis. Most people recover within one to two weeks without requiring any medical treatment. In the very young, the elderly and people suffering from medical conditions such as lung diseases, diabetes, cancer, kidney or heart problems, Influenza poses a serious risk. In these people, the infection may lead to severe complications of underlying diseases, pneumonia and death. The currently circulating influenza viruses that cause human disease are divided into two groups: A and B.