The Omicron variant has taken hold in the UK, with Prime Minister Boris Johnson warning the country faces a "huge spike" of infections this winter.
But some experts have said it is not clear exactly how this new strain will affect a population that is reasonably well-vaccinated but ageing – in contrast to the experience in southern Africa so far.
There is one certainty about the variant in the UK — it is spreading fast.
So quickly, the British government has declared a battle of "virus and vaccine" and is trying to get booster shots to every eligible adult by the end of December.
Meanwhile, the devolved nation of Scotland has asked its citizens to limit socialising in the lead-up to Christmas, as well as reintroducing social distancing in shops and hospitality venues.
Omicron now accounts for about 20 per cent of COVID-19 infections in England and almost makes up the majority of infections in London, according to the UK Health Secretary Sajid Javid.
Yesterday, Mr Javid warned that Omicron will be the dominant strain in the capital within 48 hours.
This week he told parliament there were more than 4,700 active Omicron cases, but the UK's health agency has estimated that the real number of infections is 20 times higher than confirmed cases.
Doctors warn the strain is so transmissible it will become the dominant variant not just in the UK, but the world, very quickly, and last week Mr Javid said modelling suggested there could be a million cases of Omicron in the UK by the end of the year.
"The sheer number of people impacted will have a huge impact on health care systems," Deepti Gurdasani, an epidemiologist from Queen Mary University of London, told the ABC
All bets on the British booster program
Boris Johnson's plan is to combat the variant with an ambitious booster jab program, which has seen the government pledge to offer all eligible adults a third dose by the end of the month.
It requires the country to break its own vaccination records and immunise about a million people a day.
To date, the highest daily vaccination figure was about 840,000, according to Mr Javid.
Meanwhile, the government has relaxed travel restrictions to African countries, but has reintroduced some mask mandates in some indoor venues, as well as COVID passports.
People have also been asked to work from home where possible.
But experts have mixed opinions about whether the UK's booster race will be enough to ease the burden on the country's health system.
"A vaccine-only approach isn't appropriate here because it's not going to happen in time to deal with the huge impact of such a variant, we need a multifaceted approach everywhere," Dr Gurdasani said.
Tim Spector, a professor of genetic epidemiology at King’s College London, said he was not convinced the booster program would make a huge difference in the short term.
"Now, looking at the speed of Omicron it looks like it's going to be all over before these extra people have had their booster."
Charles Bangham, director of the Institute of Infection at Imperial College London, said the UK government's plan to offer booster vaccines will still be beneficial.
"We know that the booster that is now being rolled out even faster does give a very significant boost in protection against both symptomatic disease and especially severe disease."
On Tuesday the UK reported 59,610 new COVID-19 cases – the highest daily number since July.
Hospital admissions for those with COVID are also up 10 per cent over the past seven days, while deaths have dipped slightly.
"It's a shame, I think, because we have such good surveillance systems, but despite that, we seem to be sort of sleepwalking into this crisis at a point in time," Dr Gurdasani said.
Omicron experience will be different in Europe versus Africa: experts
Some early data from South Africa that shows Omicron may cause fewer hospitalisations should be treated with caution, Professor Spector said.
"Obviously, living in Africa compared to living in a cold climate like the UK is just a different environment.
"The South African population is generally less well vaccinated and younger, whereas the UK population is older and more vaccinated."
He is the principal investigator on a central UK study and app program which monitors COVID-19 cases and symptoms.
From the small pool of data collected already about Omicron infections in the UK, it is not clear what symptoms vaccinated people will get.
It is even less clear how symptoms compare to the Delta variant among the unvaccinated, he said.
"What's also unclear is whether people have had recent infections from Delta are perhaps better protected against this," he said.
With higher levels of immunity in the population than earlier stages of the pandemic, this outbreak could be quite different to previous ones, Professor Bangham said.
"I think this current wave of Omicron is going to resemble more like a severe outbreak of influenza, which of course, we get every few years, every winter," he said.
"And again, it may be like that in years to come."
Many other countries could soon be faced with a similar predicament as the UK.
The UK's robust genetic monitoring regimes meant that it may be more aware of the spread than other countries, he said.
"The countries in Europe that have the most cases also happen to the best, the best genetic surveillance methods," Professor Spector said.
"Denmark, I think, has the highest rates in Europe, and they have probably the best per head genetic capabilities.
"It's very hard to compare countries at the moment, and if there are differences, within a few weeks, they're going to be pretty meaningless."
