https://www.npr.org/2021/12/28/1068643344/cdc-omicron-covid-19-delta-revise-estimates

Alarms that the hyper-contagious omicron variant accounted for the vast majority of new COVID-19 infections over the past couple of weeks were significantly overestimated, according to the Centers for Disease Control and Prevention.

New data released on Tuesday shows that while omicron remains the dominant variant, delta — which is the more severe strain — is still a worrisome driving force behind the current surge.

The CDC had previously reported that as of Dec. 18, 73% of new cases were linked to omicron. But on Tuesday, the agency revised those figures, slashing that estimate to 23% — a 50-point drop, suggesting that while the new variant was on the rise, it was not infecting people at the rate the CDC had projected.