It suggested that in countries such as South Africa, which have encountered different variants and have far lower vaccine uptakes than Britain, the immunity of the population will not be the same.

“By now, 19 or 20 months into the pandemic, many of us on planet Earth have very different patterns of protective immunity to Sars-Cov-2 variants and these have been shaped by prior infection, plus vaccine exposures,” Prof Altmann said.

“That’s what we mean by the term ‘immune imprinting’. I think we’ve been careful about any predictions about what omicron means to the UK, because we’re in such a different context here, in terms of an enormous background of delta caseload and higher vaccination rates.

“I was one of the people who was quite fast to say I was terrified by the mutations. And I’m still kind of terrified by them. But I’m also kind of calmed by the real life on-the-ground data as it looks like even in South Africa, with low vaccination uptake, vaccines are holding up to some extent against it.

“What it means for this country is I think we can calm down. The jury’s out. We’ve got a high level of vaccination and a backdrop of delta.”

Doctors in South Africa also said that vaccinated patients with the omicron variant are having only mild to moderate symptoms, while the country’s National Institute for Communicable Diseases said that 87 per cent of hospitalised cases were unvaccinated.