The Omicron epidemic is being driven by young, vaccinated people, according to mounting data from countries as diverse as the UK, Denmark and South Africa. 

The new variant has now been detected in more than 60 countries, including 24 in Europe, with a similar pattern of infection and characteristics being reported across the globe. 

But while the speed and the vaccine-evading properties of the virus are now established, there is as yet no firm verdict on its virulence or severity. 

"Generally those first cases are in relatively young, relatively healthy and – in the context of Europe – in relatively highly vaccinated groups," Dr Catherine Smallwood, a senior emergency officer at the World Health Organisation's Europe office, told the Telegraph. 

Data from Denmark – a world leader in genetic sequencing – shows that, of 3437 Omicron cases detected, just over 70 per cent have been among those younger than 40, according to the breakdown from the Statens Serum Institut published on Monday (Tuesday NZT). 

Some 75 per cent of these cases were in fully vaccinated individuals, the institute added, confirming that even the double jabbed can carry the virus. 

Daily cases in Denmark have surged by a third since early December, despite almost 80 per cent of the population being double vaccinated. 

The country tightened restrictions at the end of last week – introducing a midnight curfew on bars and restaurants and closing schools early for the Christmas holidays – but experts estimate Omicron could become the dominant variant as soon as Wednesday. 

Neighbouring Norway, which has so far reported 958 cases, also introduced new Covid control measures on Monday, with the Prime Minister warning that the situation is "serious". 

Preliminary data suggests the pattern of spread is, so far, similar worldwide. 

Analysis from the European Centre for Disease Control found 72 per cent of early cases were in those under 40, while the US said the majority of the 43 infections detected so far were in this same age bracket. American authorities also revealed that 79 per cent of people infected were vaccinated. 

People queue for Covid-19 booster jabs at St Thomas' Hospital, London on December 13. Photo / AP 

Professor Emmanuel Andre, head of the national reference lab for Covid-19 in Belgium, said the country is two weeks behind the UK, where Omicron cases jumped by 50 per cent on Monday and the first death with the variant was confirmed. 

"Most infections documented at this early stage are among younger age groups," he told the Telegraph, citing work, travel, sports competitions and schools as possible explanations. But Andre added that Christmas celebrations could "amplify" Omicron's spread. 

Dr Smallwood also warned that older, more vulnerable populations are likely to be infected in the coming weeks as the variant's spread picks up speed. This pattern is not especially new; it has been observed with previous strains and waves, she added. 

Smallwood also suggested that data so far suggests there is a real increase in the number of breakthrough cases in vaccinated individuals, compared to previous waves, but said it's too soon to confirm whether the variant triggers milder disease. 

"It's really important we don't get ahead of ourselves in terms of judging the severity of omicron," Smallwood said. "Because in terms of the cases we've picked up, they're in a healthier, more mobile, younger, highly vaccinated population… and we're not even that far into the disease trajectory." 

People wait for their Covid vaccinations at Soweto's Baragwanath hospital in South Africa on December 13. Photo / AP 

Experts in South Africa, where Omicron has been circulating for longer, have also urged caution on jumping to conclusions. 

There have been some suggestions that the case fatality rate has dropped to 0.5 per cent, while early data paints a picture of hospitals treating fewer people with oxygen in intensive care. 

But hospitalisations have risen steadily, with 4200 admissions on Monday – about six times the level reported three weeks ago. Statisticians have warned against over-interpreting the limited data available. 

"In 10 days there will be a much clearer picture of how the severe the new variant is around Gauteng province, as well as the evolution of mortality in the country," Professor Tom Moultrie, a demographer at the University of Cape Town, told the Telegraph, referring to the province at the epicentre of the country's Omicron wave. 

Experts also pointed to Wednesday as a potentially significant moment; the South African Medical Research Council is set to release excess death figures for the last two weeks, and it's hoped this may shed more light on the situation. 

- by Sarah Newey and Will Brown, Daily Telegraph UK