London, Dec 13 : Britain's Covid-19 alert level has been raised from Level 3 to Level 4 "in light of the rapid increase in Omicron cases," British chief medical officers have said in a joint statement. In the statement, the four chief medical officers and the National Health Service (NHS) England National Medical Director on Sunday said the emergence of Omicron "adds additional and rapidly increasing risk to the public and healthcare services." "Early evidence shows that Omicron is spreading much faster than Delta and that vaccine protection against symptomatic disease from Omicron is reduced," said the statement. The statement suggested people should continue to "take sensible precautions, including ventilating rooms, using face coverings, testing regularly and isolating when symptomatic." Level 4 means the virus is "in general circulation" and "transmission is high and direct Covid-19 pressure on healthcare services is widespread and substantial or rising." Another 1,239 Omicron cases have been found in Britain, the biggest daily increase since the Covid-19 variant was detected in the country, taking the total cases found in the country to 3,137, the UK health security agency confirmed on Sunday. Britain reported 48,854 new Covid-19 cases, bringing the total in the country to 10,819,515, according to official figures released on Sunday. The country also reported a further 52 Covid-related deaths, taking the national death toll to 1,46,439, Xinhua news agency reported. More than 89 per cent of people aged 12 and above in Britain have had their first vaccine dose, and more than 81 per cent have received both, according to the latest figures. Some 40 per cent have received their booster jab, or the third dose. /IANS