Introduction

Influenza - commonly called the ‘flu’ - is a serious and highly contagious viral illness caused by influenza A and B viruses. Its symptoms are clearly distinguishable from those of the common cold and include fever/chills, cough, headache, muscle aches and pains and fatigue. Influenza is also associated with serious complications such as pneumonia and bronchitis.

Everyone is at risk of influenza, but hospitalisations and deaths from the virus and its complications mainly occur in at-risk groups: the elderly, the young and those with chronic illnesses such as asthma and diabetes.

Influenza usually occurs in explosive, annual outbreaks that last for six to eight weeks causing significant morbidity and mortality. Every year, on average, one in ten adults and one in three children are affected by influenza, with up to 100 million people infected by the virus in the Northern Hemisphere alone. 

Influenza epidemics, where a widespread outbreak of the disease occurs, can result in the infection of between five to ten percent of the population. During an epidemic, the number of deaths from influenza or its complications can be as high as 870 per 100,0005 of the population worldwide.