Ninety years ago, tens of millions of people died in a worldwide flu pandemic, and it is a health crisis that could reoccur at any time.
As the newly appointed external chair of the Department of Health's Scientific Advisory Group on Pandemic Flu, Sir Gordon Duff's job is to ensure that the UK can cope in a worst-case scenario of this kind.
When flu emerges in several separate clusters with rapid human-to-human transmission, it is defined as a pandemic. Last century there were three such outbreaks, resulting in countless deaths, and those outbreaks have been used to model the likely outcomes of a contemporary pandemic.
Sir Gordon said: "You can learn a lot from history. We had pandemics in 1918, the famous Spanish flu in 1957 and 1968. In 1918, the worldwide deaths are estimated to have been between 20 and 40 million.
"A lot of those people died from secondary bacterial infections such as pneumonia, which couldn't be treated by antibiotics. Now we can treat those, but estimates for the UK are still alarming - anything up to 750,000 deaths."
Professor Duff studied medicine at the University of Oxford before gaining a PhD in the neuropharmacology of fever from St Thomas' Hospital Medical School in London. He went on to work at Yale University before joining the University of Edinburgh in 1984. In 1990 he took up his present post as Florey professor of molecular medicine at the University of Sheffield, where he has been research dean of the medical faculty and director of the division of genomic medicine. He received his knighthood last year.
The World Health Organisation, which grades the threat of a flu pandemic, is monitoring clusters of the virus in East Asia, but human-to-human transmission is low.
Professor Duff said that avian flu, far from being a mere scare story, was the likely source of the next pandemic.
"The thing about preparing for pandemic flu is that until it occurs we don't know what we'll be dealing with. We can follow the highly pathogenic strains of avian flu such as H5N1, but we can't know until it happens what the clinical profile will be. There's no way of making an accurate prediction about whether it will happen, when or how it will happen, but we must take it as a serious threat and make sure we are prepared."
The emergency plan, in the event of a pandemic, is based on antiviral treatment and social isolation. The advisory group's job is to keep this plan under review. Professor Duff said the group was being expanded to include more academics, give it greater independence, and ensure it kept up to date with the latest scientific information.