Up to 75,000 people could die from Covid in the next five months as the Omicron variant sweeps through the UK, scientists have warned.
Experts from the London School of Hygiene & Tropical Medicine (LSHTM) said tougher coronavirus restrictions may be needed to prevent Omicron from causing a high number of hospitalisations and deaths.
The scientists, who advise the government, said the new Covid-19 strain could cause between 25,000 to 75,000 deaths in England over the next five months.
They used experimental data to look at how Omicron may transmit as the country heads into 2022.
The experts, who also sit on the Scientific Pandemic Influenza Group on Modelling (SPI-M) or the Scientific Advisory Group for Emergencies (Sage), said the new variant could cause a high number of hospitalisations if further measures are not introduced.
They said that even if booster jabs are found to be highly effective against Omicron, a wave of infection is projected which could lead to a peak of more than 2,000 daily hospital admissions.
This would mean 175,000 hospital admissions and 24,700 deaths between December 1 this year and April 30, 2022.
For this reason, the scientists said further measures may need to be implemented in addition to the current Plan B introduced by the government in England.
The team said mask-wearing, working from home and booster jabs may not be enough, and predict a peak of daily hospital admissions of 2,400 in January.
In this scenario, bringing in control measures early in 2022 would be sufficient to substantially control the wave, reducing hospital admissions by 53,000 and deaths by 7,600.
They said measures such as restrictions on indoor hospitality, the closure of some entertainment venues and limits on the number of people who can gather in one place may be needed.
In a pessimistic scenario - high immune escape from vaccines and lower effectiveness of boosters - scientists said there could be a peak in hospital admissions around twice as high as the peak seen in January 2021, if no additional control measures are taken.
This could cause 492,000 hospital admissions and 74,800 deaths, according to the study, which has not yet been peer-reviewed.
In this scenario, the team estimates that stronger measures may be required to keep the peak number of hospital admissions below the January 2021 peak.
The scientists assumed Omicron causes the same severity of illness as Delta but did not look at the impact of measures such as mass population testing to control its spread.
They said in their paper: "These results suggest that Omicron has the potential to cause substantial surges in cases, hospital admissions and deaths in populations with high levels of immunity, including England.
"The reintroduction of additional non-pharmaceutical interventions may be required to prevent hospital admissions exceeding the levels seen in England during the previous peak in winter 2020-2021."
Dr Rosanna Barnard, from LSHTM's Centre for the Mathematical Modelling of Infectious Diseases, who co-led the research, said: "More data over the next few weeks will strengthen our knowledge on Omicron and the consequences of this on transmission in England.
"However, these early projections help guide our understanding about potential futures in a rapidly-evolving situation.
"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.
"It is crucial for decision-makers to consider the wider societal impact of these measures, not just the epidemiology."
Dr Nick Davies from CMMID, who co-led the new study, said: "These are early estimates, but they do suggest that, overall, Omicron is outcompeting Delta rapidly by evading vaccines to a substantial degree."
He told a briefing "the booster programme will substantially mitigate the impact of Omicron in England".
Dr Davies added that it was difficult to predict the true level of protection offered by two doses of AstraZeneca and Pfizer, and urged people to get boosters.
The scientists made assumptions about the levels of transmissibility and immune escape of Omicron using "S" gene target failure (SGTF) data from cases in England.
These are cases that are highly likely to be Omicron because the SGTF occurs with Omicron but not the Delta variant.
For the two immune escape scenarios considered, the team estimated the Omicron variant to be between 10% less transmissible than the Delta variant to 35% more transmissible than Delta.
Many experts have already said Omicron is more transmissible and they expect it to rapidly overtake Delta as the dominant variant.
Earlier, Eleanor Riley, a professor of immunology and infectious disease, said Omicron is spreading so fast that people are "very likely" to meet someone infected with the Covid-19 variant unless they are "living the life of a hermit".
The University of Edinburgh academic also warned "a lot of people" could still end up in hospital even if the coronavirus mutation proves to provoke milder symptoms than the Delta variant.
Prof Riley told BBC Radio 4's Today programme: "Omicron is spreading so quickly that, I think, unless you are living the life of a hermit, you are very likely to come across it in the next few weeks.
"I don't think anyone should be going around thinking they are not going to catch it, I think that situation has changed."
She added: "There is a huge 'if' about this, 'is it milder?'. I think it is very dangerous to compare data from South Africa, say, to the UK.
"Even if it is milder and, therefore, a smaller proportion of infected people end up in hospital, given that so many people are going to come across this virus, even a small proportion of a lot of people is a lot of people in hospital."
BDST: 1945 HRS, DEC 11, 2021