The omicron variant is now considered the most dominant version of the coronavirus — making up 73% of new COVID-19 infections last week in the U.S., according to new data released by the Centers for Disease Control and Prevention on Monday.
The new estimates capture cases for the week that ended on Dec. 18.
The new estimates underscore just how rapidly it has spread across the U.S. As of a week prior, Dec. 11, it was detected in only 12.6% of positive COVID-19 cases that were sampled.
The CDC said it was working on revising some of the earlier numbers after officials finish analyzing more samples of the strain.
Omicron is even more prevalent in some parts of the U.S., including the Pacific Northwest, the Great Lakes, the Southeast, a cluster of states centered on Texas, and New England, where it is above 90% of samples.
Since the end of June, the delta variant of COVID-19 had been the primary strain of the virus causing the majority of U.S. infections, with more than 99% of new coronavirus cases being delta in the past several months.
Much about the omicron variant, scientists say, still remains uncertain — including whether the new variant causes more- or less-severe illness.
"All of us have a date with omicron," Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told The Associated Press. "If you're going to interact with society, if you're going to have any type of life, omicron will be something you encounter, and the best way you can encounter this is to be fully vaccinated."
Omicron has already triggered a wave of new infections across the U.S. and the world, with health officials warning of its extraordinary transmissibility. Early data suggests that while omicron can more easily evade immune protection and booster shots than prior strains, those infected may be less likely to experience severe disease and hospitalization.
However, "even if it has a somewhat lower risk of severity, we could be having a million cases a day if we're not really attentive to all of those mitigation strategies," outgoing National Institutes of Health Director Francis Collins told NPR over the weekend.
Getting booster shots appears to still offer substantial protection against severe disease and death from omicron, according to health officials.