The Omicron variant of the novel coronavirus could lead to around half a million hospitalizations and close to 75,000 deaths in the United Kingdom this winter, if no additional control measures are taken, according to new modeling.

Scientists at the London School of Hygiene and Tropical Medicine, or LSHTM, said in a worse-case scenario, daily infections during January could be twice as high as they were during January 2021, when cases reached record levels.

The preprint study, which is yet to be peer reviewed, set out a number of scenarios that took into consideration differing levels of natural immunity and vaccine effectiveness in the context of the highly mutated variant.

Omicron is thought to cause a higher number of reinfections in people who have previously recovered from COVID-19, according to separate data from South Africa. Scientists are still gathering data on vaccine and booster efficacy against the variant.

In the most optimistic scenario, where there are low levels of so-called immune escape and booster shots are highly effective, the winter wave will lead to a peak of 2,000 daily hospital admissions, with 175,000 hospitalizations and 24,700 deaths between December 2021 and April 30.

The most pessimistic scenario, in which there is a high level of immune escape and boosters are less effective, projects around 492,000 hospitalizations and 74,800 deaths during the same period.

"These are early estimates, but they do suggest that, overall, Omicron is outcompeting Delta rapidly by evading vaccines to a substantial degree," said LSHTM epidemiologist Nick Davies, who co-led the research. "If current trends continue, then Omicron may represent half of UK cases by the end of December."

Both scenarios assume no additional lockdown or social distancing measures, beyond those that are currently in place in the UK, which recently reinstated a mask mandate and a proof of vaccination rule for some venues, as well as a work-from-home recommendation.

The UK government has been reluctant to revisit more disruptive measures, instead opting for a strategy that focuses on vaccination and other drug interventions, including a pilot program for at-home antiviral pills.

But the LHSTM said if vaccines prove less effective at preventing severe illness against Omicron, more draconian measures should be considered to take pressure off health services.

In the most optimistic scenario, the researchers said measures including restrictions on indoor hospitality, the closure of some entertainment venues, and restrictions on gathering sizes would be "sufficient to substantially control the wave", reducing hospitalizations by 53,000 and deaths by 7,600.

Stronger measures would be needed to control the wave predicted in the worst-case scenario.

"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," said Rosanna Barnard, an LSHTM epidemiologist who co-led the research.