With Britain firmly in the grip of the delta blues, concerns about other variants had largely slipped off the radar.

So it was unexpected when last week the Government insisted that doubly-vaccinated travellers from France would still need to quarantine for ten days because of the "persistent presence of the beta variant".

The beta variant, formerly known as the South African variant, was rattling around Britain last year before it was convincingly out-competed, first by the alpha (Kent) variant, then more recently the delta (Indian) strain. Just a dozen or so cases are now reported each week.

Scientists were initially concerned about beta because it carries two troublesome mutations, one which increases transmissibility, and a second which helps it evade immunity.

One study in February found it lowered AstraZeneca vaccine efficacy to just 10.4 per cent, a finding which prompted South Africa to halt the rollout of the British jab.

So a fully-jabbed traveller would have barely any more protection against the variant than someone unvaccinated. 

% of covid cases sequenced by variant type

But while that might sound worrying, a quick look at the figures in France tells a less gloomy story. Far from rising, cases of the beta variant have been falling in the country since May.

According to the global science initiative Gisaid, France has reported just 93 cases of the beta in the past four weeks, with the variant making up just 3.5 per cent of infections.

To make matters more confusing, many of these cases were not from mainland France, but from the French overseas departments of La Reunion and Mayotte, 6,000 miles away in the Indian Ocean, where the beta variant is dominant.

It is no wonder then that on Tuesday, France’s Europe minister Clément Beaune dubbed Britain’s quarantine rules as "excessive" and "unscientific". At home, British scientists tend to agree.

Paul Hunter, professor in medicine at the University of East Anglia, said: "The beta variant is in steep decline in France, and it looks like the delta variant has taken over. It’s pretty much the dominant strain everywhere in Western Europe.

"As soon as delta gets established, beta packs its bags and goes somewhere else, we’ve seen that in the UK. It will probably be extinct in a year or so.

Proportion of B.1.351 (Beta) variant among sequenced cases in European Economic Area

"I was quite surprised when I read the Government was leaving quarantine measures in place. I suspect within the next month we won’t have any cases of beta in Metropolitan France at all, so I do think we’ve over-reacted to this."

The decision regarding France is all the more baffling because countries with far higher rates of beta are currently not facing further restrictions. 

In Spain, nine per cent of infections are beta, a rise of 0.6 per cent from the previous month, while the variant makes up 13 per cent of cases in Greece, where it is also increasing slightly.

But even with rising prevalence, experts believe beta simply is not fit enough to outcompete delta or establish a firm foothold in Britain.

Jonathan Ball, professor of molecular virology at the University of Nottingham, said: "In terms of general fitness, the beta variant is a bit of a lightweight.

"It’s a variant that has traded off its own fitness for the ability to escape antibodies, and it is clearly being out-competed by other variants.

Cases are approaching January peak

"The science suggests this is a virus that can escape immunity, so we need to be cautious, particularly in people who have only had a single dose. But the data in France would suggest that it’s not particularly good at spreading."

Professor Adam Finn, a member of the Joint Committee on Vaccines and Immunisation (JCVI), also said he was "not really quite sure" about the thinking behind the French restrictions.

Yet some experts believe the pre-emptive measures may help avert further lockdowns.

Dr Julian Tang, honorary associate professor/clinical virologist at the University of Leicester, said: "In the early part of the pandemic in January 2020, when the UK’s response was to wait and see, it then resulted in a national lockdown in March."

For a country emerging tentatively from restrictions, perhaps being ultra-alert to importing new problems is a sensible option.

But while the delta variant is dominant, we can be relatively confident it will keep beta at bay. It may be that the recent rise of delta could end up posing less harm than good.