The UK is facing a substantial wave of Omicron infections in January without further restrictions, scientists say.
The number of deaths from the variant by the end of April could range from 25,000 to 75,000 depending on how well vaccines perform, they said.
But the experts behind the study said there was still uncertainty around the modelling, reports BBC.
In the worst-case scenario tougher restrictions may be needed to stop hospitals being overwhelmed, they said.
The work by the London School of Hygiene and Tropical Medicine (LSHTM) is not a crystal ball. It does not say what will happen with the Omicron variant of coronavirus but gives a range of possible outcomes.
High uptake of the booster dose is likely to mitigate the impact of the Omicron wave, the researchers said.
Dr Nick Davies, one of the researchers, said Omicron was spreading “very fast”, was “quite concerning” and was likely to be the dominant form of the virus in England by the end of the year.
The report – from an influential group of disease modellers among those advising government – says the number of people infected is currently doubling every 2.4 days in England.
That is despite the country having high levels of vaccination and is faster than the original form of the virus spread when nobody had protection.
Dr Davies said: “Based on what we’re seeing we can expect there to be a large wave of Omicron in the UK.”
However, the most uncertainty is around how well the vaccines and boosters will keep people out of hospital.
Early real-world studies by the UK Health Security Agency estimated two doses of a vaccine gave limited protection against developing Omicron symptoms, but a booster dose raised it up to 75%.
The LHSTM study assumes Omicron is less severe than previous variants if you have been vaccinated and takes into account the current Plan B measures.
In the most optimistic scenario the numbers being admitted to hospitals every day would be 40% lower than the peak last winter. In the most pessimistic scenario it would be nearly twice as high.
But the report said “the majority of scenarios” concluded that with current measures there would be more admissions than last winter.
At the peak of the coronavirus wave in January 2021 there was a seven-day average of nearly 60,000 infections and more than 1,200 deaths per day.
What are the scenarios?
In the most optimistic scenario, which assumes Omicron has low immune escape and booster jabs are highly effective, the model projects between 1 December and 30 April in England there will be:
* 20.9 million infections
* 175,000 hospital admissions
* 24,700 deaths
In the most pessimistic scenario, which assumes Omicron has high immune escape and booster jabs are less effective, the model projects between 1 December and 31 April in England there will be:
* 34.2 million infections
* 492,000 hospital admissions
* 74,900 deaths
Dr Davies said: “I think our projections are worrying, it doesn’t paint an optimistic picture.”
While the research looked at the impact of introducing new restrictions on the Omicron wave, Dr Davies said tougher curbs were “terrible” for people’s physical and mental wellbeing and needed to be carefully weighed up.
The modelling warns that in the pessimistic scenarios it could require measures that restrict who we meet, what businesses can open and staying at home where possible to prevent intense pressure on the NHS.
More data is needed before the true picture of where the UK is heading becomes clear.
Dr Rosanna Barnard, one of the researchers, said: “In our most optimistic scenario, the impact of Omicron in the early part of 2022 would be reduced with mild control measures such as working from home.
“However, our most pessimistic scenario suggests that we may have to endure more stringent restrictions to ensure the NHS is not overwhelmed.
“Mask-wearing, social distancing and booster jabs are vital, but may not be enough.
“Nobody wants to endure another lockdown, but last-resort measures may be required to protect health services if Omicron has a significant level of immune escape or otherwise increased transmissibility compared to Delta.”
The research has been published online but has not been through the formal process of being reviewed by other scientists.
Earlier, Prof Eleanor Riley, professor of immunology and infectious disease at the University of Edinburgh, said that “unless you are living like a hermit” it was very likely that you would come into contact with someone infected by Omicron in the coming weeks as it was spreading so quickly.