Millions of birds have died. How to stop humans dying, too

Over the past couple of years the largest outbreak of avian influenza (h5n1) in recorded history has torn across the planet. The virus, which is deadly to birds, has devastated wild and domesticated flocks alike. Attempts to stop transmission have seen hundreds of millions of birds culled on farms since the strain was first identified in 1996. Wild bird deaths are probably in their millions at least. The danger is that, as the virus mutates, a bird pandemic becomes a human one. Precisely how h5n1 will adapt and spread is impossible to predict. But the time to prepare is now.

In the past year the virus has spread in a range of mammals, and it is now rife among dairy cattle in America. This has led to several confirmed infections in farm workers. So far, these have been mild and isolated. However, many more cases in cows and people are thought to be going undetected, because of gaps in surveillance.