Universities are abruptly closing classrooms during finals week with infections multiplying at a fast rate. Both t he NBA and NHL have had to postpone games, and the NFL had its worst two-day outbreak since the start of the pandemic, with dozens of players infected.Outside the U.S., the president of the European Union said omicron will become the dominant variant in a month and declared that "once again, this Christmas will be overshadowed by the pandemic."Scientists around the world are racing to understand omicron, which has a large number of worrisome mutations in important regions of its genetic structure that could affect how it spreads from person to person.