According to agency data, omicron accounted for about 59 percent of all U.S. infections as of Dec. 25. Previously, the CDC said the omicron variant comprised 73 percent of all cases for the week ending Dec. 18. But that number has now been revised to 22.5 percent of all cases.

The omicron variant is highly transmissible and spreading rapidly, resulting in surges of infections even among people who are vaccinated. However, people who are vaccinated, and especially those who have received booster shots, are well protected against severe disease from the variant, experts say, meaning it poses the greatest risk to the unvaccinated.

The new estimates mean that while a majority of new infections are attributed to the omicron variant, the delta variant has not been sidelined, and still accounts for about 41 percent of infections.