The first justification for deliberately engineering a bird flu virus that is easily transmitted from ferret to ferret is that it alerts the world to the potential hazard to public health posed by the virus, thus countering a dangerous complacency about it; the second is that it might aid attempts to produce a vaccine against or a treatment of the illness. But critics argue that the research actually increases the risks of disaster rather than reduces them, either by inadvertence or (if the technique for engineering viruses fell into the wrong hands) by malice.

The scientific journals that were to publish the research were faced with a dilemma. Should they, or should they not, omit information about the technique of engineering the virus? Did freedom trump caution? In the end, they decided to omit the information in the name of safety, but to give it to bona fide researchers who asked for it.

Of course the threat of a pandemic of a new and fatal viral disease would be a very blunt instrument for anyone who wanted to use it, because he could not insure himself or his friends against it. But perhaps there are enough nihilists in the world to make the danger a real one.

How worried, then, should we be by bird flu? I confess that I am not sure. And not knowing how anxious I ought to be makes me… well, anxious.