Nearly two years into the COVID-19 pandemic, the world raced Friday to contain a new coronavirus variant potentially more dangerous than the one that has fueled relentless waves of infection on every continent.

A World Health Organization panel named the variant “omicron” and classified it as a
highly transmissible virus of concern, the same category that includes the predominant
delta variant, which is still a scourge driving higher cases of sickness and death in Europe and parts of the United States.

“It seems to spread rapidly,” President Joe Biden said of the new variant, only a day after celebrating the resumption of Thanksgiving gatherings for millions of American families and the sense that normal life was coming back at least for the vaccinated. In announcing new travel restrictions, he told reporters, “I’ve decided that we’re going to be cautious.”