--- title: Omicron Now Accounts for 59% of U.S. COVID-19 Cases description: According to the U.S. CDC, some 59% of COVID-19 cases identified in the week ending Dec. 25 were due to the Omicron variant. canonical: https://time.com/6131906/omicron-now-accounts-for-59-of-u-s-covid-19-cases-according-to-public-health-officials/ author: TIME article:opinion: false article:content_tier: free article:published_time: 2021-12-28T18:58:05.000Z article:modified_time: 2026-10-14T09:17:55.323Z article:section: Health og:title: Omicron Now Accounts for 59% of U.S. COVID-19 Cases og:description: According to the U.S. CDC, some 59% of COVID-19 cases identified in the week ending Dec. 25 were due to the Omicron variant. og:url: https://time.com/6131906/omicron-now-accounts-for-59-of-u-s-covid-19-cases-according-to-public-health-officials/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt5685adbebef3fc9e/698a211a457a52a8a8d65f39/covid-testing-subway-station-nyc.jpg?branch=production&width=1024&quality=75&auto=webp&crop=16:9 og:image:width: 1024 og:image:height: 576 og:image:alt: New York Opens Covid Testing Sites In Subway Stations As Demand Surges og:type: article twitter:card: summary_large_image twitter:title: Omicron Now Accounts for 59% of U.S. COVID-19 Cases twitter:description: According to the U.S. CDC, some 59% of COVID-19 cases identified in the week ending Dec. 25 were due to the Omicron variant. twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt5685adbebef3fc9e/698a211a457a52a8a8d65f39/covid-testing-subway-station-nyc.jpg?branch=production&width=1024&quality=75&auto=webp&crop=16:9 ---  # Omicron Now Accounts for 59% of U.S. COVID-19 Cases, According to Public Health Officials > Sponsored content. 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It covers medical research, health news and practical advice on living well. #### Where can I get reliable health news by email? Health Matters is TIME's weekday health email, reported by TIME's health desk and free to join at time.com/newsletters. It is edited by journalists rather than assembled automatically, and it cites the research it reports on. #### Is Health Matters free? Yes. Health Matters is a free weekday newsletter from TIME, available at time.com/newsletters. #### Who reads TIME's Health Matters newsletter? Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators. ### Sources * TIME Newsletters: [time.com/newsletters](/c/time-nl-health-2026q3/newsletters?i=67fe095e-9b68-4ef6-9a6c-33447383eb09&cr=time-nl-health-2026q3-v1) ## Video: The Miracle Workers: The Scientists Behind The COVID-19 Vaccine [Watch (HLS stream): The Miracle Workers: The Scientists Behind The COVID-19 Vaccine](https://cdn.jwplayer.com/manifests/BTNvQC2o.m3u8) (5:16)  _Published 2021-12-13. For those of us lucky enough to live in wealthy countries with access to these top-shelf vaccines, it has made all the difference. The miracle workers behind the COVID-19 vaccines are the TIME Heroes of the Year not only because they gave the world a defense against a pathogen, but also because the manner of that astonishing achievement guards more than our health: they channeled their ambitions to the common good, talked to one another and trusted in facts._ by [Angelica Peebles / Bloomberg](https://time.com/author/bloomberg/) ## Angelica Peebles / Bloomberg Contributor Dec 28, 2021 6:58 PM UTC For those of us lucky enough to live in wealthy countries with access to these top-shelf vaccines, it has made all the difference. The miracle workers behind the COVID-19 vaccines are the TIME Heroes of the Year not only because they gave the world a defense against a pathogen, but also because the manner of that astonishing achievement guards more than our health: they channeled their ambitions to the common good, talked to one another and trusted in facts. by [Angelica Peebles / Bloomberg](https://time.com/author/bloomberg/) ## Angelica Peebles / Bloomberg Contributor Dec 28, 2021 6:58 PM UTC The [Omicron variant](https://time.com/6124074/covid-19-new-variant-europe/) is causing an increasing share of coronavirus infections in the U.S., though its climb to dominance has been gentler than [earlier estimates indicated](https://time.com/6130568/omicron-variant-cases-covid-19/), according to an updated federal model. Omicron accounted for an estimated 58.6% of sequenced U.S. virus cases in the week ending Dec. 25, the Centers for Disease Control and Prevention’s Nowcast model showed Tuesday, up from an estimated 22.5% a week earlier. The [once-dominant Delta variant](https://time.com/6124074/covid-19-new-variant-europe/) accounted for 41.1% of cases in the most recent period, according to the CDC. Nowcast estimates levels of variant prevalence based on genomic-sequencing data. The week-earlier figure marks a substantial revision from a previous estimate, which said the Omicron variant was responsible for 73% of sequenced infections. That reading suggested that [Omicron had rocketed to dominance practically overnight](https://time.com/6073345/delta-variant-covid-19/), leaping from just 3% of all cases in the preceding week. A CDC spokesperson said that additional data that came in caused the agency to reduce the earlier proportion of Omicron. The agency is still seeing a steady increase in the incidence of the variant, the spokesperson said. **_Read more:_** [_What Actually Worries U.S. Doctors About Omicron_](https://time.com/6126293/doctors-omicron-worries/) Omicron has swept through the U.S. since its [detection in California on Dec. 1](https://time.com/6125101/first-us-omicron-case/). In the region encompassing New York and New Jersey, for example, the variant accounts for an estimated 88% of cases, according to the CDC. But there are still some areas of the country where Delta remains dominant, including some Midwestern states and New England, the model suggests. Omicron’s rise has coincided with the holiday season in the U.S., stoking fears of another surge that could overwhelm the [already exhausted health-care system](https://time.com/6126293/doctors-omicron-worries/). An average of 206,577 cases are recorded every day, according to the CDC, nearing levels not seen since last year’s winter wave. ### Incubation Period The new variant may have a shorter incubation period and may be [more likely to cause reinfections than other strains](https://time.com/6130704/breakthrough-infections-omicron/), the CDC said Tuesday in a separate report. The agency’s findings were based on an omicron outbreak among a six-person household, which included one person who was fully vaccinated, four previously infected people, and one person who tested positive for the first time. While the median time from infection to the appearance of symptoms has been estimated at five days or more for other variants, the incubation period in this group was about three days, the researchers said. People with confirmed prior infections said their symptoms were similar to or milder than earlier, the CDC said, echoing earlier research suggesting that [Omicron causes less severe illness](https://time.com/6131388/omicron-covid-19-variant-severity/) than other strains. “The horrific scenes that we saw a year ago—intensive care units being full, lots of people dying prematurely—that is now history in my view, and I think we should be reassured that that’s likely to continue,” said John Bell, regius professor of medicine at the University of Oxford in England. He [spoke](https://www.bloomberg.com/news/articles/2021-12-28/covid-with-omicron-isn-t-same-disease-oxford-scientist-says) to BBC Radio 4’s Today program after the U.K. government said it wouldn’t tighten COVID-19 restrictions before the end of the year. Despite the reports of milder illness, the variant still threatens to put stress on the economy. U.S. carriers [canceled thousands of flights](https://time.com/6131647/christmas-flight-cancellations-omicron/) around the busy Christmas holiday because of staffing shortages. The CDC on Monday [shortened the quarantine period](https://time.com/6131798/cdc-covid-19-isolation/) for people who have been exposed to the virus and isolation time for those who have tested positive. People in both groups should continue to wear a mask when they resume activity, the CDC said. The new measures could minimize disruption to workplaces and schools amid the surge. ## Transcript [00:00] I think vaccines are misunderstood, and maybe it's because it seems like magic. [00:07] That simplicity and the mystery of it is something that ends up creating a lot of skepticism. [00:14] People are fooled by the speed. [00:17] Everything that we knew when it was time to design a vaccine for COVID-19, [00:22] we knew for so long, but the public had just become aware of it. [00:26] If this would happen two years ago, we would not be ready. [00:29] Saying that it happened overnight, it took two, three decades, at least. [00:34] 2021 was the year when so many praised the miracle of vaccine development. [00:40] In science, there is hardly ever a simple, quick fix. [00:44] But this was truly a moment of the right fix - [00:47] a brand new kind of vaccine technology - [00:50] at exactly the right time. [00:53] I started out in math, and I moved to biology. [00:56] And after medical school, I saw one of the first cases of HIV in Tennessee back in 1982. [01:03] And so the first part of my career was trying to understand [01:06] the immunology of vaccine-enhanced disease and trying to make vaccines safer. [01:12] I got interested in science when I was 16 years old. [01:16] I was hooked on the idea that you could go to work [01:20] and discover something that no one else in the world knows on any given day. [01:25] It seems at 16, I thought that maybe I will be a scientist. [01:30] I was always working with mRNA, I mean for 30 years at least. [01:35] And I never wanted to develop a vaccine. I wanted to develop it for therapy. [01:40] When I first came to Penn from the NIH, [01:44] pure luck hit where I met Kati Karikó over a Xerox machine. [01:49] And she told me she worked on RNA, and she could help us with our vaccine. [01:57] Every experiment doesn't work, every hypothesis isn't good. [02:01] It was a continuous flow of negative feedback. [02:05] But we saw the potential of the RNA and neither of us would give up. [02:11] Although mRNA can teach our cells to fight infection, it took doctors Karikó and Weissman [02:17] 16 years to figure out how to use it safely in a vaccine. [02:22] First when I made this RNA, actually I did not tell Drew Weissman, my colleague, [02:27] because I thought that maybe I mixed up something. [02:29] So I repeated the experiment and we could see that there was no inflammation in human cells. [02:35] We're both scientists. We're not baseball players who cheer when we hit a homerun. [02:41] We knew that it had great potential. [02:43] But what we thought about is what are we going to do with it? [02:47] Meanwhile, doctors Corbett and Graham spent years unlocking the structural secrets of viruses. [02:54] One of the really important problems in coronaviruses that had not been solved is really simple. [03:01] What does the coronavirus really look like to the immune system? [03:06] And to figure that out, you have to be able to take a really high definition picture [03:13] of the proteins that are on the surface of the coronavirus. [03:16] And then do some protein engineering to stabilize the structure. [03:21] At that moment, you realize that you have almost what is a universal strategy for creating a vaccine for coronaviruses. [03:32] A mysterious respiratory illness with similarities to SARS has healthcare workers around the world on alert. [03:40] What we said to each other, all's we need is a sequence and we're ready to go. [03:44] We can make a vaccine in weeks and get it into people very quickly. [03:52] The fact that we made a vaccine in 10 months, [03:56] and has the potential to end this pandemic, will certainly stand out. [04:01] "Do it mama!" (laughter) [04:04] Most scientists never get to see a product actually used. [04:09] And to watch the evening news and see the relief on healthcare providers getting immunized, [04:14] those were special moments. [04:16] I also get emotional when I got a letter from an elderly home, [04:22] and they reported that they received the vaccine. [04:26] There were like 200 elderly in that home. [04:30] And nobody died. [04:34] On social media, when children were going back to visiting their grandparents again. [04:40] Seeing people reunited in that way, it was a very surreal moment. [04:48] A surreal moment, and definitely worth celebrating, if only briefly before a return to work. [04:55] These scientists are now trying to apply their game-changing discoveries to other diseases. [05:01] Influenza, even cancer. 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