The coronavirus has mutated many times since it emerged in China in 2019, according to epidemiologists. On Friday, South Africa reported it had identified a new variant, which it said was driving a new wave of infections there. It is not clear whether it is same variant as the one identified in Britain.
Most of these variants are not significant or widespread. But as the number of people who have been infected — and, presumably, have developed some immunity — increases, the pressure on the pathogen to mutate also increases. Some of the new variants can be more transmissible or lead to more severe illness than earlier versions of the virus.
“This is potentially serious,” Jeremy Farrar, an infectious disease expert who is director of the Wellcome Trust, said in a statement last week. “The surveillance and research must continue, and we must take the necessary steps to stay ahead of the virus.”
For weeks, Mr. Johnson has struggled to balance his response to the virus with pressure not to further damage the economy. The government instituted a graduated scale of tiers, placing Manchester, Liverpool and other northern cities, where the infection rates were higher, in the most restrictive tier. Life in London remained mostly unchanged.
In November, as infection rates began to climb across the country, Mr. Johnson imposed a new nationwide lockdown. That ignited speculation in British tabloids that he would be forced to “cancel Christmas.” Instead, he vowed to relax restrictions on social mixing for a five-day period around Christmas to allow families to get together.
But last week, amid signs that London had become a new hot spot, Mr. Johnson placed the capital and most of the southeast in Tier 3, the highest level of restrictions. He clung to his promise of a Christmas reprieve from Dec. 23 to Dec. 27, even as he implored people to keep family gatherings brief and small.
“Have yourself a merry little Christmas,” Mr. Johnson said last week, announcing the half measures, “but this year alas, preferably a very little Christmas.”