Down, up, down again: the stock market, like the rest of us, doesn’t know how to react to the omicron variant. The FTSE 100 index fell by more than 3pc on Friday, when the news emerged, recovered some of its losses on Monday, then fell again yesterday. It now stands 3.4pc below its close on Thursday last week.

What should readers do? Sell everything on the basis that the market is being slow to cotton on to the danger, rather as it was in February last year, when it needed the virus’s arrival in Europe to make investors take notice? Sell certain stocks and buy others in an attempt to exploit the market’s well documented inability to respond to sudden, dramatic events on a rational stock-by-stock basis?

Buy the market as a whole, via a tracker fund, in the hope that it has overreacted? Or do nothing? 

Regular readers will not be surprised to hear that we incline towards the last option. We certainly don’t advise a wholesale exit from the markets. As we said in February last year, just after the Covid crash began, we had no way to know that the virus would cause such disruption so quickly and in every corner of the world.

It was, according to the information we had then, also possible that the outbreak would fizzle out, as earlier ones of viruses such as Mers and Sars had done, and that markets would quickly recover.

Those who sold everything in the expectation that they would be able to buy back in more cheaply would face the disagreeable task of forcing themselves to do so at higher prices, and the natural urge to put off that task would in all likelihood only worsen the financial pain.

Selective buying and selling makes sense in theory but requires careful scrutiny of the reactions of individual share prices and the degree to which the fundamentals of the business are reflected, or overlooked, in those share price moves.

For private investors who have established a portfolio of stocks that they intend to form the bedrock of their long-term savings and have chosen strong, durable companies, there is almost certainly no need to make changes.

All that said, one opportunity does stand out to this column. While the share prices of some vaccine makers have shot up in the past few days – BioNTech has gained 14pc since before news of omicron and 54pc since our advice to hold three weeks ago, while Moderna, which we frustratingly advised readers to sell in January, is 27pc to the good since news of omicron – AstraZeneca has only continued a losing streak that began with the publication of its third-quarter results earlier this month.

 Its shares are 12pc lower than before those results and 2.7pc below last Thursday’s close.