The new omicron variant of COVID-19 has nearly made delta obsolete, as it was responsible for 95.4% of all new cases in the week that ended Jan. 1, according to CDC data released Tuesday.
It took only about a month for the new variant to displace delta, as the first case of omicron was detected in the United States on Dec. 1 and it was responsible for just 0.6% of new cases for the week that ended Dec. 4.
Omicron was responsible for 8% of cases by Dec. 11, 37.9% of cases by Dec. 18, and 77% of cases by Dec. 25.
Delta is still dominant in parts of New England and the Plains, but omicron is dominant everywhere else, according to CDC data.
The rise of omicron has coincided with a record surge in new COVID-19 cases, as the seven-day average for new cases stood at 316,277 on Dec. 29.
Multiple studies have shown that omicron's rapid spread may be due to the variant's ability to evade immunity offered by both vaccines and previous infection.
While it may be spreading faster than previous variants, omicron has been associated with milder disease.
A study conducted by Discovery Health in South Africa, where omicron was first identified, found that hospital admissions for adults with the new variant were 29% lower than for those with delta.
Researchers at the LKS Faculty of Medicine at The University of Hong Kong found that omicron replicates 70 times faster than delta in the human bronchus, but 10 times slower in lung tissue, which may explain why it spreads more rapidly but is responsible for less severe disease.
Vaccines are still effective against illness from omicron, according to a University of Copenhagen study that found a booster shot offered 86% protection against symptoms and 98% protection against severe disease.
New hospital admissions for COVID-19 were up to 10,185 on Dec. 28, an increase over the 6,592 that were admitted on Dec. 1, when omicron was first detected. The seven-day average for new deaths was 1,100 on Dec. 29, an increase over the 879 deaths that occurred on Dec. 1.