The long predicted influenza pandemic appears to be upon us, with more than 20 cases reported in the US at this writing. Last year, the World Bank predicted a pandemic would affect the world economy by a 5pc drop in output.

The US government has declared a health emergency, with Homeland Security chief effectively saying “Don’t panic.”

The danger is a kind of pandemic protectionism spreads around the world, adding to its economic woes. Already pork from Mexico has been banned by China and Russia. The ban has now been extended to Texas, California and Kansas. We can be sure that is only the beginning.

A serious 1918 type of pandemic, which killed millions around the globe, would really challenge the world economy and set it back a decade at least.

Let us hope it doesn’t come to that.