Residents in London and southeast England must adhere to new emergency lockdown restrictions, as the country fights a wave of COVID-19 infections from a new fast-spreading strain of the virus. 

According to a report from Bloomberg, 16.4 million Britons are impacted by the new stay-at-home orders that went into effect on Sunday. The move overturns previous plans from Prime Minister Boris Johnson to ease restrictions for the holidays.

“When the virus changes its method of attack we must change our method of defense,” Johnson said at a news conference Saturday. “Without action the evidence suggests infections would soar, hospitals would become overwhelmed and many thousands more would lose their lives.”

As Bloomberg reports, the new strain appears unique to the U.K. and “can spread significantly more quickly than previous strains in circulation and is behind a huge surge in infections in recent days.” Sixty percent of London’s cases in the past week, which doubled in comparison to prior weeks, were caused by the new strain. 

“There is no current evidence to suggest the new strain causes a higher mortality rate or that it affects vaccines and treatments, although urgent work is underway to confirm this,” England’s Chief Medical Officer Chris Whitty said. “Given this latest development it is now more vital than ever that the public continue to take action in their area to reduce transmission.”

The new restrictions shut down all non-essential shops to close and require 31 percent of the country’s population to stay home until the rules are revisited on Dec. 30. Residents are also discouraged from traveling and mixing with other households.