I’VE BEEN having to notify people that I’ve just come back from northern Italy, where I’m hoping that I picked up nothing other than a few good meals and some packets of reasonably-priced tobacco.

I mention this because yesterday morning the health secretary at Westminster, Matt Hancock, advised everyone in my position to “self-isolate” if they had flu-like symptoms, or – if they’d been in one of the dozen or so Italian towns that have been quarantined – even if they didn’t.

Since I practically never leave the house anyway, and don’t seem to have any of the warning signs, this is no enormous hardship. But it shows how difficult it is to avoid the impact of remote events in an era of globalisation.

A decade ago, the Steven Soderbergh film Contagion imagined a global pandemic which, like the coronavirus, started in Asia and quickly spread throughout the world. With luck, the huge casualties and civil disorder it depicted won’t be brought about by this virus, but even if it fails to become a pandemic, it’s already had a dramatic effect on more than public health or travel.

Italy, which had had around 300 reported cases by yesterday, was already screening airline passengers last week, measuring their temperature on arrival. Not very effectively, actually; several people from my plane missed the check (and passport control) by inadvertently walking through the wrong door.

Unlike China, where an autocratic government can shut down whole cities and impose tight restrictions, there is a limit on what a free society can manage. On my trip, for example, I arrived in Turin, but left from Milan, thus passing through two huge cities, two major railway stations, and two sizeable airports.

The primary concern, naturally, is public health; a pandemic – even if it has a mortality rate of “only” around two per cent – still has the potential to kill millions. That was roughly the ratio for Spanish flu in 1919, which killed 30 million people. But the economic impact has been as dramatic – even while the virus remains relatively contained.

At the beginning of the week, the Dow Jones lost 1,000 points in a day (which amounts to all its gains for the year). The Italian stock market dropped six per cent, shares in companies such as Apple, which rely on Chinese manufacturing, were down around four per cent, while travel firms got hammered: EasyJet lost a sixth of its total valuation on Monday alone.

An outbreak of illness in a Chinese province most British people probably hadn’t heard of a few weeks ago has, more or less directly, led to a drop in sales of 85 per cent at stores in Bicester Village, an outlet centre in Oxfordshire.

There are suggestions that there will be a shortage of toys this Christmas unless Chinese factories get back to normal in the next couple of weeks. Romania is attempting to quarantine anyone who has visited Lombardy, and my daughter tells me that Lidl in Turin (where she lives) has run out of pasta after panic buying.

The coronavirus is having a huge impact on Western economies as well as China’s, even if the disease doesn’t spread more widely. It is a largely unexpected and unavoidable natural event bound to occur now and then. But what it illustrates is that the prosperity and productivity of the Chinese worker has a direct effect on retail staff in Bicester or, for that matter, Brazilian soybean prices or Scotch whisky exports.

And the major, altogether avoidable, contributors to creating such obstacles to increased prosperity, in China and at home, are barriers to trade. That’s why Brexit or UK/US trade talks, dull stories compared with deadly pandemics, have comparable importance.

The UK must have as much flexibility to deal with other countries as it has had with the EU which, far from being a free trade area, erects protectionist barriers (as well as being a diminishing proportion of the global market). Tariff costs are borne, not by foreign countries, but by domestic importers and therefore consumers.

Restrictions on the movement of goods and people necessitated by this outbreak are a sharp illustration of the economic costs of constraints on trade. And at least with trade policy we already know the prescription to avoid the damage.