The flu outbreak may be winding down in Mexico and causing fewer deaths than feared, but health officials now fear that a more virulent version will return to kill millions.

In the spring of 1918, North Americans were complaining about an unseasonable flu that was sweeping through several cities. They and the rest of the world were still blissfully unaware of what was in store for later that year: a pandemic that would kill 50 million people, or by some estimates many more - certainly more than the Great War that was still raging.

The World Health Organization (WHO) this week remained on the verge of declaring a pandemic of the H1N1 swine-associated flu
virus. Public-health bodies and scientists have made progress in starting to understand the outbreak, but major questions remain about how severe the disease will get.

Damned if you do, damned if you don

If an influenza pandemic is declared, investigations by New Scientist suggest that global preparedness for a pandemic is extremely patchy.

There were signs that swine flu posed a human pandemic threat over a decade ago, yet no one paid any attention.