IN 1918, a virulent new strain of influenza swept the world, killing at least 20 million people before it disappeared. It was the worst human epidemic on record.
Yet on a patient-by-patient basis the virus responsible for this slaughter was not so lethal. Untreated, HIV kills virtually everyone it infects. Ebola and hantavirus kill about half. The 1918 flu virus finished off between 3 and 5 per cent: nearly everyone who contracted it survived.
The problem was that, unlike Ebola and HIV, the virus was airborne, extremely contagious and capable of rapidly infecting hundreds of millions. As any successful currency…
