Omicron Is Now the Dominant COVID-19 Variant in the U.S.

covid map omicron



On December 28, the CDC significantly revised its estimate of the number of Omicron-driven COVID-19 infections in the United States. While it is still the dominant variant in the U.S, during the week ending on December 18, the CDC says it accounted for only 22.5% of all cases, not 73%.

Key Takeaways

  • Omicron is now responsible for about 73% of COVID-19 cases in the U.S., according to the CDC.
  • The WHO said Omicron is much more transmissible than Delta, with cases doubling every 1.5 to 3 days.
  • The severity of illness from Omicron infection is not yet well understood. However, the dramatic uptick in cases may drive a surge in hospitalizations.  

Omicron is now the dominant COVID-19 variant in the United States, comprising an estimated 73% of cases, according to data from the Centers for Disease Control and Prevention (CDC).

The estimates capture cases for the week ending December 18, nearly 20 days since the variant was first detected in the U.S. In the week prior, the variant accounted for only 12.6% of positive cases that were sampled.

In some parts of the country, including regions of the Northwest and Southeast, Omicron comprises more than 95% of the circulating virus.

"I am flabbergasted at how quickly this has happened,” F. Perry Wilson, MD, MSCE, a physician at Yale Medicine and researcher at the Yale School of Medicine, told Verywell. “It completely blows anything we've seen thus far out of the water in terms of transmissibility.”

“Essentially, everyone who's going to get Omicron is going to get it within the next couple of months,” he said.

According to the World Health Organization (WHO), Omicron is spreading "significantly faster than the Delta variant," with cases doubling every 1.5 to 3 days.

Researchers are still working to understand whether the variant drives more or less severe illness. In the meantime, medical experts maintain that the best bet for protecting oneself is to get vaccinated and boosted.

“Severe cases, hospitalizations, and deaths, or what the vaccines were designed to prevent and they are holding up well in that regard,” Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, told Verywell.

Hospitals May Take a Big Hit

Omicron has already spurred a surge in case rates this winter. But the immunity landscape this year looks quite different than the last, thanks to the availability of COVID-19 vaccines for people older than 5 years.

Early data from lab studies and real-world observation indicate that Omicron is better at evading the immune defenses, even in those who are vaccinated. However, boosters appear to restore antibodies to a protective level.

Wilson said that for vaccinated people who have breakthrough infections, they can expect to experience only mild flu-like symptoms. “We still see even among people who aren't boosted that the vast majority of hospitalizations are among people who are unvaccinated,” he added.

Nearly 38% of Americans aged 5 and above are not yet vaccinated, and only a third have received a booster shot.

Wilson said that COVID-19 case rates may top records from last winter. However, hospitalizations and deaths may not reach such heights because the majority of the U.S. population has at least some vaccine- or infection-induced immunity.

Still, given how quickly the variant has taken hold in the country, already-strained hospitals may become even more overwhelmed. Data from other countries indicated that surging Omicron case rates have led to a bump in severe cases. In the United Kingdom, for instance, hospitalizations have increased by about 30% week over week.

“That's what scares me most—the healthcare system can only absorb so much and we’ve been absorbing a lot of late,” Wilson said.

More than 80% of U.S. counties are currently experiencing “high” COVID-19 transmission. In some areas of the country, vaccination rates remain low and hospitals have more limited capacity, meaning people there are more vulnerable to adverse outcomes.  

What Health Authorities Are Doing to Mitigate Spread

In a speech this week, President Joe Biden announced that his administration will purchase 500 million at-home rapid COVID-19 tests to be made available for free and ready to be delivered in January. The administration will also open 10,000 new vaccination sites and additional testing sites in hard-hit areas, with the first opening in New York City this week.

In January, people who purchase at-home tests may have the cost reimbursed by their health insurer. Biden said there will also be tests available for uninsured individuals.

“As we move into the next phase of this pandemic, being able to test at will is going to be really important to minimize the disruption of the virus causes to our lives,” Adalja said.

During the holiday season, as Americans are traveling and gathering with loved ones, tried-and-true mitigation strategies—like getting tested for COVID-19, wearing a mask, and isolating when necessary—will be key to slowing the spread. The CDC recommends against traveling until fully vaccinated.

“People should be vaccinated and ideally boosted before they're gathering together in this current environment,” Wilson said.

Today, the Food and Drug Administration authorized Pfizer’s oral drug to treat COVID-19. Antiviral treatments may be taken early in a COVID-19 infection to minimize the severity of infection and tamp down hospitalizations. Wilson said such medications will be a “game-changer” in the coming weeks and months.

What Can We Expect Next?

It may be too soon to know how Omicron will shape the future of the COVID-19 pandemic. But given the current rate of spread, Wilson predicts nearly everyone will be exposed to the virus in the next few months.

“Viruses can burn themselves out when they spread too quickly,” Wilson said. “They basically burn through the population like wildfire and then all of a sudden everyone has some pretty decent immunity.”

“I'm worried about the suffering that this will entail, particularly among people who are not adequately vaccinated or people who vaccines aren't effective for,” he added.

A CDC modeling analysis projects that the daily number of cases could peak as soon as January.

Compared to last January, when cases topped 250,000 per day, Omicron could drive a daily case rate of up to 1 million without sufficient mitigation, Francis Collins, retiring director of the National Institutes of Health told NPR.

The CDC warns that given the likely increase in infections, the number of people with severe illness from COVID-19 could be substantial.

What This Means For You

Experts say the best way to protect yourself and others from the spread of Omicron and other viral variants is to be fully vaccinated and receive a booster six months after completing your primary regimen. You can find appointments near you at

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. COVID Data Tracker.

  2. Centers for Disease Control and Prevention. COVID Data Tracker.

  3. Centers for Disease Control and Prevention. COVID Data Tracker.

  4. Centers for Disease Control and Prevention. Potential Rapid Increase of Omicron Variant Infections in the United States.

By Claire Bugos
Claire Bugos is a health and science reporter and writer and a 2020 National Association of Science Writers travel fellow.