Outside In | Four takeaways about the deadly flu virus... and why historians are concerned

As Chinese families were celebrating the Lunar New Year on February 11 1918, almost exactly 100 years ago, the Western World was edging grimly out of the bloodiest world war ever fought. Around 20 million soldiers and civilians were dead.

At that moment no one realised that in a matter of weeks, one of the world’s worst global pandemics was about to break out. By the spring of 1919, as the third and final wave of so-called “Spanish Flu” swept across the globe, around a third of the world’s population had been infected, and close to 100 million had died.

Since then, by comparison, every threatened pandemic ended up being (in comparison) a damp squib. And in 2018, despite reports worldwide of the worst flu season in decades, no one expects anything like Spanish Flu – which never originated in Spain, just for the record. In an average year, about 5 million people get infected with one flu virus or another, and an average of 10 per cent of these – about 500,000 die. But during our Sars epidemic in 2003, a total of 8,000 people were infected worldwide, and just 775 people died. Look back at mortality data for 2003 and deaths attributed to pneumonia (all Sars deaths were recorded as pneumonia) and there is no blip to give a hint of the panic that swept Hong Kong and the world in the spring of 2003.

Similarly with Ebola, which erupted in Guinea almost a decade later. By today, there have been 11,300 deaths worldwide due to Ebola. Even Aids has only killed 1.2 million in the 30 years we have been panicked by it.

So what lessons should we take away from all this? First, damp squibs or not since 1918, there is little doubt that the next true global pandemic will erupt somewhere not too long from now. Sometime soon, it is probable that one of the existing menu of avian or pig flu viruses that cause most flus, will do two things: it will morph into something hugely more virulent; and it will discover how to hop from birds (or pigs) to humans.

What made the H3N2 virus that sat at the heart of Spanish Flu so vicious was that it was particularly good at mutating, and it killed about 20 per cent of those it infected. A normal flu kills perhaps 1 per cent. What made the 1347-50 Black Death so lethal was that it killed up to 60 per cent of those it infected. The only reason it killed fewer people (about 75 million) than the Spanish Flu was that the world had fewer people then. About a third of the world’s population died, most in western Europe.