Economic impact of swine flu
There's so much we don't know about the swine flu story - the potential economic impact is just one of them.
Many in the markets and elsewhere are now trying to estimate what the eventual economic cost of the outbreak might be. It's safe to say that none of them has a clue.
The scary starting point for these calculations is a study by the World Bank last year, which suggested that another truly global flu epidemic would end up costing nearly 5% of world GDP - or more than $3 trillion.
That's assuming a pandemic on the scale of the 1918 "Spanish Flu" outbreak, which infected around one third of the world's population and killed 50 million. Helpfully, the report concludes that a hit of this magnitude would throw the world into a depression.
Of course, that could happen. But experts who know more about viruses than I do (not a small list*) are still suggesting that the chances of such a catastrophe are small. We do have anti-viral drugs now that weren't available. And, they tell me, some version of flu already infects tens of millions of people a year, killing at least half a million of them, without leading to a pandemic on that scale.
What about the more recent, and less alarming, example of Severe Acute Respiratory Syndrome (Sars) in China and Hong Kong? That killed more than 700 people in 2003, and (according to the Asia Development Bank) cost the region between $18bn and $60bn in lost output - or 0.5-2.0% of regional GDP.
Many say it will be less this time, because the world is better prepared. And this virus seems a bit easier to treat. I'll leave that to others to judge.
But as Julian Jessop, chief international economist at Capital Economics, points out, even in the Sars case the costs turned out to much less than initially feared. If you look at the retail sales data in China it's a blip, but nothing more than that. A lot of the initial fall was made up later, when people made the purchases that they had previously put off.
Ill-informed optimism is no better than ill-informed gloom. But if we are looking at something on the scale of the Sars issue now, my guess is that the same will be true this time. The costs will be less than some now fear.
Some have said that the impact will be greater, because the global economy is already in such a fragile state. At first glance that seems sensible - you could say that our global economic immune system is in a weak state to shrug this illness off.
But I suspect the opposite is true, that the economic costs of this virus might actually be less than it would otherwise have been, because some of the output that might have been lost to flu has already been lost to the recession.
To put it bluntly, if unemployed people are forced to stay at home for a few weeks, that has a smaller economic cost than if they were all in work. And if people are already going out less to restaurants, cinemas and the like, the fall in consumption due to flu may be smaller than it would have been as well.
Of course, you can't push this argument too far - any pandemic that killed millions of the working age population would have an enormous long-term impact on our potential output, regardless of whether they happened to be out of work when they died.
I fear this blog is turning into a parody of economic analysis at times like this, as I debate the finer economic points of a potential humanitarian catastrophe. But after all, this is a blog about economics.
Assuming that this is more a Sars style outbreak, with widespread but short-term disruption to normal economic activity rather than millions of deaths, it is possible that the impact - in the midst of recession - will be less visible than it would have been a few years ago.
But don't get me wrong, with the global economy as weak as it is, it would be far, far better not to be facing this threat at all.
* as evidenced by an earlier version of this post, which wrongly specified a particular version of the flu. Apologies.