What health officials do know is that omicron is already infecting scores of Americans, dealing a psychological blow to an exhausted nation and provoking new policy challenges. The outbreak has been fueled both by omicron, which is spreading at astounding speed, and the older delta variant.

“It’s breathtaking to watch the rate at which everything is increasing right now,” said S. Wesley Long, medical director of diagnostic microbiology at Houston Methodist.

He predicted that omicron could overtake delta to make up 100 percent of his health system’s coronavirus cases by January. “I don’t think any of us thought that we would ever see anything transmit faster than delta,” Long said. “Now we have the omicron variant that’s even more transmissible.”…

News of the new variant is proving disorienting for many Americans, as mask mandates are reinstituted in some Democratic-led states, parents deal again with school closures, and families question whether they can safely gather for the holidays.