Health Secretary Sajid Javid disclosed the estimate in the U.K. House of Commons on Monday, as the government made fresh calls for all eligible adults above the age of 18 to get a COVID-19 booster shot. The country’s National Health Service (NHS) has classified Omicron as a “national incident”–level threat.

The new estimate of 200,000 daily Omicron cases dwarfs the U.K.’s official daily total of 54,661 new COVID infections reported Monday. While about 4,700 Omicron cases have been confirmed in the U.K. as of Monday, Javid said the new variant accounted for 20% of cases in England—and some 44% of cases in London where, he said, it would likely become the dominant strain within 48 hours.

The new estimates indicate the U.K. should soon surpass South Africa as the epicenter of the highly contagious Omicron variant—if it has not already. South Africa reported 13,992 COVID infections in the past 24 hours, but the number of new cases had for several days been below the peak of 22,391 on Thursday, suggesting infections were plateauing, and could be headed for decline.

“Omicron is indeed very infectious and seems to be spreading more rapidly in the U.K. than in South Africa,” Paul Hunter, a professor of medicine at the University of East Anglia, said about Omicron’s rise. He added that the latest R number in South Africa is about 2.2, while in the U.K. this figure is estimated at 3.7, which indicates a doubling every two to three days.

The U.K.’s and South Africa’s differing trajectories could be attributed to high numbers of earlier infections in South Africa. One recent study in Gauteng, South Africa’s most populous province, found that 72% had been previously infected with COVID-19. These previous infections offer some natural immunity, and may mask the severity of the Omicron variant outbreak, South African scientists said.

Vaccine drive

The U.K.’s NHS website crashed on Monday after a surge in demand from people trying to book a booster shot, while the government set up hundreds of vaccination sites in soccer stadiums and racecourses across the U.K. in a push to offer booster shots to all adults by the end of the year.

The NHS will have to distribute 18 million booster jabs before the end of 2021 if it hopes to meet Prime Minister Boris Johnson’s target, which many NHS leaders doubt will happen. The booster shot’s popularity skyrocketed after news emerged that the Omicron variant partially evaded immunity from a double vaccination of Pfizer, leaving “fully vaccinated” people with just 22.5% immunity, one study found.

The U.K. is not alone in launching a massive booster push to stave off Omicron. Public health authorities in Denmark and Norway predict the Omicron variant will come to the Nordics next with cases and hospitalizations inching upwards. The Norwegian government called on the military and pharmacists to assist with booster shot vaccinations which it hopes to give to everyone above age 45 by mid-January.