Just over a dozen years ago, a bird flu virus known as H5N1 was charting a destructive course through Asia, North Africa, and the Middle East, ravaging poultry in apocalyptic numbers and killing 6 in 10 humans known to have contracted it.

The overall human death toll was low — in the hundreds — but scientists and government officials feared that the virus could ignite a human pandemic reminiscent of the catastrophic 1918 Spanish flu. Emergency plans were drafted, experimental H5N1 vaccines were created and tested, antiviral drugs were stockpiled.

And then … nothing happened.