Influenza is one of the oldest and most common diseases known to man. It can also be one of the deadliest. Influenza is a serious infection of the breathing passages causing symptoms of fever, cough, sore throat, runny nose, headache, muscle aches and extreme fatigue. Most people recover completely within 1-2 weeks. However, compared with other viral respiratory infections like common colds, flu causes more severe complications such as pneumonia particularly in children, elderly people and other vulnerable groups.
Flu epidemics kill hundreds of thousands of people a year and cause millions of cases of illness.
Influenza is a major public health concern and a major drain on economic productivity, as sick employees take time off work, and on the health service. But what was potentially so frightening about the isolation of this new strain of flu, H5N1, was that this was a purely bird virus against which most humans would have no defence. There would be no immunity in the human population against this potential killer because humans had previously not been exposed to it and so had not built up antibodies against it. This meant the virus had the potential to rage through the human population. The emergence of H5N1 raised the spectre of a flu pandemic .