The UK has more new Covid-19 cases than France, Germany, Italy and Spain combined - CNN

Johnson has strayed from much of the European Union in his approach; while a number of countries on the continent have introduced vaccine passports, England halted its original plan to do so.

And the country's early vaccination success risks being undone by a stuttering rollout of booster shots and shots for children.

"Exceptional policies lead to exceptional outcomes," Deepti Gurdasani, an epidemiologist at Queen Mary University in London, told CNN.

This is a consequence of opening everything up."

"We're approaching winter, and things are only going to get worse," she added.

Some things may yet shut back down; Johnson's spokesperson admitted on Monday that a "challenging" winter lies ahead, and the Prime Minister has refused to rule out a return of mask mandates or stronger restrictions to protect the country's National Health Service (NHS) in the coming weeks.

But experts -- including Johnson's own health care chiefs -- are clamoring for a more urgent change in approach.

The NHS Confederation, which represents providers of the service, urged the government on Wednesday to move to its "Plan B" raft of measures, which would include European-style vaccination passes and more mask mandates.

But the government has ruled out that move for now, only insisting it was closely watching the case figures.

"There's a whole series of ways (in which) we're out of line with western Europe and the rest of the world," said Martin McKee, professor of European Public Health at the London School of Hygiene & Tropical Medicine.

(Because) there's no evidence that we are."

A stuttering vaccine rollout

The driver behind Britain's renewed optimism in the new year was its vaccination program, which outpaced most countries in its initial scale and set the narrative for what Johnson portrayed as Britain's triumphant emergence from the pandemic.

But the country is struggling to repeat those early successes as it attempts to vaccinate adolescents and roll out booster shots to elderly and at-risk people.

"England's booster rollout is failing to keep pace with the rollout of first and second vaccine doses," John Roberts, a consultant at the Covid-19 Actuaries Response group which tracks vaccination figures, warned in a statement on Monday.

"It's clear that accelerating the booster rollout is vital to reduce the pressure on health services and minimise Covid-related deaths this autumn and winter," he said.

Several European countries, including France and Italy, have rolled out Covid-19 passes and required vaccination for healthcare workers, while many more still employ mask mandates in crowded spaces that the UK does not.

"Vaccine passes have an important role to play; the French and the Italian experience show that they do," McKee said.

Cases have remained low in both countries since the measures were introduced.

Health care is devolved in the UK and vaccine passes have been announced in Wales and Scotland.