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More than 40 people in the U.S. have been found to be infected with the omicron variant so far, and more than three-quarters of them had been vaccinated, the chief of the CDC said Wednesday. But she said nearly all of them were only mildly ill. In an interview with The Associated Press, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said the data is very limited and the agency is working on a more detailed analysis of what the new mutant form of the coronavirus might hold for the U.S. (Stobbe, 12/9)

"The disease is mild" in most cases so far, Walensky told AP. Coughing, congestion and fatigue make up the bulk of reported symptoms. Though one person was hospitalized, there have been no deaths so far, per AP. Data remains limited, but the CDC is preparing an analysis on Omicron's likely impact in the U.S., Walensky added. "What we don't yet know is how transmissible it will be, how well our vaccines will work, whether it will lead to more severe disease," she told ABC's "This Week" on Sunday. (Chen, 12/8)

With the omicron variant continuing to spread in a number of countries, including the U.S., scientists have been anxiously awaiting data to answer this question: How well will the vaccines work against this new variant? On Tuesday night and Wednesday morning, scientists in South Africa and Germany released preliminary results from two small studies that begin to provide answers. The studies haven't been peer-reviewed. But together, their data strongly suggest the vaccines will be much less effective at stopping infections from the omicron variant but will still likely offer protection against severe disease. The study in Germany also indicates that a third shot, or a booster, will partially recover the effectiveness of the vaccines, at least for a few months. (Doucleff, 12/8)

The need to understand omicron’s true threat is so urgent that data is leapfrogging the usual channels. Papers are being shared even before they are made available on preprint servers, with research findings posted on laboratories’ websites or on Twitter. The laboratory experiments offer an early glimpse of how omicron behaves. But such research has limitations. Scientists are exposing the virus, or in some cases a “pseudovirus” that has the superficial features of the virus, to blood samples from people with different levels of vaccination and antibodies. That does not predict, necessarily, how the virus will spread in the general population. (Johnson and Achenbach, 12/8)

A prevailing theory as to how the omicron variant emerged so suddenly and jam-packed with mutations is that it was cultivated in an immune-compromised person — possibly someone with untreated HIV — with an extended coronavirus infection. That proposal seems especially plausible to a team of scientists at Stanford, who treated a patient diagnosed with uncontrolled HIV and COVID earlier this year, and saw a striking development of mutations in the coronavirus over just 15 days. (Allday, 12/8)

A lot is still unknown around Omicron, but a worrying trend has become clear: This variant sure is spreading fast. In South Africa, the U.K., and Denmark—countries with the best variant surveillance and high immunity against COVID—Omicron cases are growing exponentially. The variant has outcompeted the already highly transmissible Delta in South Africa and may soon do the same elsewhere. According to preliminary estimates, every person with Omicron is infecting 3–3.5 others, which is roughly on par with how fast the coronavirus spread when it first went global in early 2020. (Zhang, 12/8)

The World Health Organization on Wednesday said the highly mutated omicron variant of Covid-19 could change the course of the pandemic. The exact impact is “still difficult to know,” WHO Director-General Tedros Adhanom Ghebreyesus said at a media briefing from the group’s Geneva headquarters. Scientists across the world are scrambling to determine just how contagious and lethal the mutated virus has become. (Constantino, 12/8)

Human blood samples and the substance that makes fireflies glow are among the tools that scientists are using for early clues about whether Covid-19 vaccines retain their effectiveness against the new Omicron virus variant. (Loftus, 12/8)

When South African scientists announced they had detected a new coronavirus variant with a worryingly high number of mutations, they were applauded for how quickly they were able to spot it. The country was praised for having a robust genomic sequencing program, which allowed them to identify the potentially worrying properties of the variant now known as Omicron. (Kottasova and Shveda, 12/9)