London, Dec 20 : The number of people dying due to the Omicron variant of Covid-19 in the UK rose to 12 on Monday from seven reported on Sunday. On December 13, Prime Minister Boris Johnson had announced the first death due to Omicron in the country. The latest figures from the UK Health Security Agency also show that 104 people have been admitted to hospitals with confirmed Omicron infection, the Independent reported. Some 12,133 confirmed cases of Omicron were also reported on Sunday. However, these figures are likely to be undercounting the true numbers, as not all Covid cases are checked in labs to ascertain if they are the Omicron variant, the report said. Meanwhile, experts on the government's Scientific Advisory Group for Emergencies (SAGE) have warned that there are probably thousands of new Omicron infections every day in England alone. The SAGE team has advised the government to limit social contact and ban mixing of households during Christmas. Health Secretary Sajid Javid has also refused to rule out another lockdown before Christmas, the Daily Mail reported. According to Deputy Prime Minister Dominic Raab, the government "can't make hard, fast guarantees" that there will not be a Christmas lockdown, the BBC reported. "I'm not going to trail things when decisions haven't been made," he said, when asked whether England can expect more restrictions in the coming days. This comes as cases of the Omicron variant have risen by 50 per cent in just 24 hours to 37,101 as the UK Health Security Agency confirmed a further 12,133 cases on Monday. Health officials also briefed the Cabinet on Sunday that more measures are required to stop hospital admissions soaring above 3,000 per day in England. Johnson had earlier warned of a "tidal wave of Omicron" in the country. As the highly transmissible variant is known to evade vaccine efficacy, the country set a new target to administer booster dose to all by the end of December, from the earlier January. A yet-to-be peer-reviewed study by London School of Hygiene & Tropical Medicine (LSHTM) has also projected that under the assumption of low immune escape, the UK will see 24,700 deaths, while in the case of high immune escape, the country will witness 74,800 deaths. /IANS