The rapidly spreading omicron variant is now the dominant Covid strain in the U.S., representing 73% of sequenced cases, according to data published Monday by the Centers for Disease Control and Prevention.
Omicron has displaced the previously dominant delta variant, which the CDC says is now an estimated 26.6% of sequenced cases for the week ending December 18. Just one week earlier, delta made up 87% of cases to omicron’s 12.6%, the data shows.
The omicron Covid-19 variant was first detected in southern Africa in late November and labeled a “variant of concern” by the World Health Organization on Nov. 26. It’s not clear when exactly it first arrived in the U.S. Though California was first U.S. state to confirm an omicron case in the country on Dec. 1, the CDC has said a patient developed symptoms earlier on Nov. 15.
While the variant has proven to be extremely transmissible, much remains unknown about the severity of the illness it causes.
In some parts of the country, the share of omicron cases is higher than the nationwide figure of 73%. The CDC estimates it makes up more than 90% of cases in portions of the Northwest, South, Southeast, and Northeast.
The CDC had previously published data for the week ending Dec. 11 showing that omicron represented 2.9% of cases, but has revised that estimate for that period upward.
This is a developing story. Please check back for updates.