What is pandemic flu?

Pandemic flu is a type of influenza characterised by its rapid spread to affect most countries in the world.

It is caused by the emergence of a new flu virus, one that we will have had no previous exposure to, and to which few people, if any, will have immunity. While the symptoms may be similar to that of seasonal winter flu, our lack of immunity means symptoms are likely to be more severe resulting in high death rates.

Sobering stats
Whether or not a new pandemic flu will be caused by an avian or bird flu is not certain. Much of our understanding of pandemic flu comes from experience of the three major flu epidemics of the last century and evidence suggests that recent pandemic flu viruses originated in birds. The global pandemic of 1918 is estimated to have killed more people than the First World War, a sobering statistic, an estimated 20-40 million lives in all. But as pointed out by the UK Department of Health, most estimates of the impact of a future pandemic are based on extrapolations from previous pandemics. They don't allow for the fact that the modern world is very different from a century ago with significant improvements in nutrition, healthcare and opportunities for intervention. The actual impact of a pandemic may be very different from predictions.