China Flu seasons outbreak 2018
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.

The second takeaway? While the attrition from a new and truly lethal pandemic would be appalling, the chances are that it would kill a smaller proportion than Spanish flu. The 1918 pandemic was not extraordinary simply because of its virulence. The timing was equally appalling, as was the state of medical knowledge back then. The hugest mortality rates were among soldiers fighting in the trenches in Northern Europe, where medical services were horribly challenged, and where the opportunity was high for the virus to move quickly through dense and insanitary populations of weak and malnourished men. Mortality was also awful in Europe's city slums, where poverty was acute and medical services miserable.

Comment: There is evidence that in the run up to the Black Death, changes in weather patterns had already lead to great famine: New Light on the Black Death: The Cosmic Connection

Whatever the shortcomings of the present treatments for our annual flu seasons, they are light-years superior to the treatments known or deliverable in 1918, so mortality rates should be significantly lower. But we have to remember that even if survival rates are higher, the sheer size of the world population today would make for sobering mortality rates. As the Centres for Disease Control in the US noted recently: "Even with modern antiviral and antibacterial drugs, vaccines, and prevention knowledge, the return of a pandemic virus equivalent in pathogenicity to the virus of 1918 would likely kill more than 100 million people worldwide."

Comment: And antibiotics are proving to be less and less effective: Top UK doctor warns of antibiotic apocalypse

Takeaway number three? While we can be optimistic that perhaps a smaller proportion of sufferers might die, we can be almost certain that the global cost would be comparatively horrendous. The global economy was horribly emaciated in 1918 after four years of the first world war, so there was little to lose in economic terms compared to today. Studies both by Brookings Institution and the World Bank over the past decade have reached similar conclusions: even a mild pandemic is likely to cost the global economy US$300 billion or more, while a severe one could wipe out US$3 trillion or more.

And takeaway number four concerns risk-assessments: all this talk of pandemic threats reminds me of how appalling we all are at getting a sensible perspective on the truly grave threats that face us, and where we should best spend our money to minimise them.

While 500,000 deaths a year due to flu is a sobering number, we should remember that 800,000 die every year from malaria, and 2.4 million from diarrhoea. Of the total 56 million deaths every year, around a quarter - about 14 million - are due to smoking cigarettes. Sars killed a total of less than 800 people worldwide, yet in Hong Kong, the panic it caused cut air travel for the year by 15 per cent, while for months retail sales crashed, and restaurants and cinemas sat empty.

Comment: No, 14 million deaths a year are blamed on smoking, whereas the actual cause of death is due to something else entirely, such as diet, stress and so on. And as they discovered during the plague years, it could actually be one of your best defences: Pestilence, the Great Plague and the Tobacco Cure

The same difficulty in managing mortality risk sits in many other areas. Do you remember how demand for air travel slumped after Malaysian Airlines flight MH370 went missing somewhere over the Indian Ocean? Does no one remember that you are 100,000 times more likely to die on a motorbike than in an aircraft, and 50,000 times more likely to die on a bicycle.

As we quite properly worry about coping with a record flu season, and the likelihood of a massive pandemic sometime soon, we should remember that other more mundane threats need much more immediate financial (and policy) attention. Carrie Lam Cheng Yuet-ngor was right to set aside HK$500 million to help hospitals to cope with our unusually severe flu season. But HK$500 million was about right. She should concentrate the billions on other more grave challenges - like attracting and training enough nurses to care for our elderly.

David Dodwell researches and writes about global, regional and Hong Kong challenges from a Hong Kong point of view

This article appeared in the South China Morning Post print edition as: The matters of life and death