"Early evidence shows that Omicron is spreading much faster than Delta and that vaccine protection against symptomatic disease from Omicron is reduced," U.K. health authorities warned.
Britain's COVID alert level has been increased from Level 3 to Level 4 "in light of the rapid increase in Omicron cases", British chief medical officers said in a joint statement on Sunday.
The four chief medical officers and the National Health Service (NHS) England national medical director 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.
They 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."
Most boosters administered per 100 people:— Edouard Mathieu (@redouad) December 11, 2021
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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 (UKHSA) confirmed Sunday.
Britain reported 48,854 new coronavirus cases, bringing the total number of coronavirus cases in the country to 10,819,515. The country also reported a further 52 coronavirus-related deaths. The total number of coronavirus-related deaths in Britain now stands at 146,439, with 7,413 COVID-19 patients still in hospital.
Over 89 percent of people aged 12 and over in Britain have had their first dose of vaccine and more than 81 percent have received both doses, according to the latest figures. More than 40 percent have received booster jabs, or the third dose of a coronavirus vaccine.