EXPLAINER: Are new coronavirus strains cause for concern?
A man walks past a closed shop on Regent Street in central in London, Sunday, Dec. 20, 2020. Millions of people in England have learned they must cancel their Christmas get-togethers and holiday shopping trips. British Prime Minister Boris Johnson said Saturday that holiday gatherings can’t go ahead and non-essential shops must close in London and much of southern England. Johnson imposed a new, higher level of coronavirus restrictions to curb sharply spreading infections in the capital and other areas. (Stefan Rousseau/PA via AP)

A man walks past a closed shop on Regent Street in central in London, Sunday, Dec. 20, 2020. Millions of people in England have learned they must cancel their Christmas get-togethers and holiday shopping trips. British Prime Minister Boris Johnson said Saturday that holiday gatherings can’t go ahead and non-essential shops must close in London and much of southern England. Johnson imposed a new, higher level of coronavirus restrictions to curb sharply spreading infections in the capital and other areas. (Stefan Rousseau/PA via AP)

Dec. 20, 2020 01:17 PM EST
A person walks through Cardiff city centre, Sunday Dec. 20, 2020. In Wales, authorities said they decided to move up a lockdown planned for after Christmas and people must stay at home from 12:01 a.m. Sunday. The move will largely scrap Christmas gatherings in line with the rules for southern England. (Ben Birchall/PA via AP)

A person walks through Cardiff city centre, Sunday Dec. 20, 2020. In Wales, authorities said they decided to move up a lockdown planned for after Christmas and people must stay at home from 12:01 a.m. Sunday. The move will largely scrap Christmas gatherings in line with the rules for southern England. (Ben Birchall/PA via AP)

Dec. 20, 2020 10:15 AM EST
Christmas shoppers in Oxford city centre England, Sunday Dec. 20, 2020. Millions of people in England have learned they must cancel their Christmas get-togethers and holiday shopping trips. British Prime Minister Boris Johnson said Saturday that holiday gatherings can’t go ahead and non-essential shops must close in London and much of southern England. (Steve Parsons/PA via AP)

Christmas shoppers in Oxford city centre England, Sunday Dec. 20, 2020. Millions of people in England have learned they must cancel their Christmas get-togethers and holiday shopping trips. British Prime Minister Boris Johnson said Saturday that holiday gatherings can’t go ahead and non-essential shops must close in London and much of southern England. (Steve Parsons/PA via AP)

Dec. 20, 2020 11:51 AM EST