Man is the only creature that can contemplate, and enjoy the contemplation of, his own extinction. One of the means by which he might disappear from the face of the earth, at least in the imagination of the writers of pulp fiction, is by the development, either by chance or design, of a fast-spreading and fatal new virus against which he has no resistance.

The emergence of bird flu fifteen years ago conjured up visions of a viral Armageddon. It was previously unknown and it was dangerous. It gave rise to the archetypal health scare, that is to say a panic about a remote possibility that was much more frightening than more real, constant but everyday dangers with which we are so familiar that we ignore them.

Bird flu was frightening because the case-fatality rate (the proportion of people who died having contracted the disease) was high and there was no treatment for it. Fortunately, though, its communicability from bird to man was low, and from person to person virtually unknown. According to a recent paper in The Lancet, 344 of 583 people known to have contracted it in the last 15 years died of it, a very tiny absolute number by comparison with the total numbers of deaths in the world during that period.