Influenza, or ‘flu’, is a common infectious disease that causes huge problems worldwide due largely to its constantly evolving nature. While most of the health burden of flu is caused by yearly seasonal epidemics, occasionally, new, more pathogenic strains can emerge, often from a non-human source such as birds or pigs. These new strains can cause pandemic spread of the disease, such as in the swine flu outbreak of 2009. To find out more about this complex virus, Helen Albert speaks to epidemiologist and flu expert Dr James Rudge from the London School of Hygiene & Tropical Medicine.

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