Experts had been saying that more information on the omicron variant was expected in the weeks following its detection.
Now, about a month since the new COVID variant was identified in South Africa and two weeks since it was first recorded in the U.S., what do we know?
Chicago's top doctor said that while we are still learning about the variant and research continues to develop, an early look at the latest data has led to some findings so far.
Here's a breakdown of what we know.
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Is omicron more severe than delta or other COVID variants?
Chicago Department of Public Health Commissioner Dr. Allison Arwady said Tuesday there is increased confidence that omicron "is likely to spread quickly" and even faster than the delta variant, which is behind the latest surge in the U.S.
"The early data suggests that this is probably, you know, maybe two to two-and-a-half times as easy to spread, as contagious as the delta variant," she said.
CDC Director Rochelle Walensky said Wednesday that early data suggests omicron is more transmissible than delta, with a doubling time of about two days.
According to an analysis Tuesday of data from South Africa, where omicron is driving a surge in infections, the variant seems to not just spread more easily from person to person, but is better at evading vaccines while causing less serious illness.
The data also shows, however, that while case numbers are rising, hospitalizations are not increasing at the same rate, leading the scientists to believe that the risk of hospitalization from omicron may be lower than delta or earlier variants. Hospital admissions for adults diagnosed with COVID-19 are 29% lower compared to the wave that South Africa experienced in mid-2020, after adjusting for vaccination status, according to the analysis.
But the World Health Organization's COVID-19 technical lead, Maria Van Kerkhove, said Wednesday that increased transmission will result in increased hospitalizations that burden health-care systems, some of which will fail.
“Omicron is spreading at a rate we have not seen with any previous variant. We are concerned that people are dismissing omicron as mild,” WHO Director-General Tedros Adhanom Ghebreyesus said. “Surely we have learned by now that we underestimate this virus at our peril.”
Arwady said she's "feeling pretty confident" that the variant will lead to more breakthrough cases and reinfections in those who have already had COVID, but the severity of those cases remains unclear despite early breakthrough cases in the Midwest showing mild symptoms, if any.
"We think based on what we're seeing now, omicron is unlikely to be more severe than delta, which is which is very, very good news, but I'm still skeptical of claims that there's significantly reduced severity," Arwady said. "So great news, it doesn't look like it's making people sicker than what we have now, but I do know there are a lot of people who feel like this is really not making people sick at all and that is not yet something that my team feels that the data shows."
For unvaccinated populations, particularly those most susceptible to COVID, Arwady anticipates "accelerated transmission and then a rising number of hospitalizations for severe illness."
Even if omicron proves milder on the whole than delta, it may disarm some of the life-saving tools available and put immune-compromised and elderly people at particular risk as it begins a rapid assault on the United States.
"We know that people infected with omicron can have the full spectrum of disease, from asymptomatic infection to mild disease, all the way to severe disease to death," Van Kerkhove said.
And if a dueling surge of both delta and omicron hits, experts fear hospitals and staff won't be able to withstand the increase.
“Our delta surge is ongoing and, in fact, accelerating. And on top of that, we’re going to add an omicron surge,” said Dr. Jacob Lemieux, who monitors variants for a research collaboration led by Harvard Medical School.
“That’s alarming, because our hospitals are already filling up. Staff are fatigued,” leaving limited capacity for a potential crush of COVID-19 cases “from an omicron wave superimposed on a delta surge.”
Will the omicron variant change vaccine efficacy or lead to more breakthrough cases?
The White House on Wednesday insisted there is no need for a lockdown because vaccines are widely available and appear to offer protection against the worst consequences of the virus.
Arwady said the city is continuing to push for vaccinations and booster shots for that same reason, though an increase in breakthrough infections is expected and there are heightened concerns for the unvaccinated.
"We do think at this point, vaccines are very likely to continue to protect against severe disease, but because there will be probably more transmission that makes it harder to control efforts," she said. "And it puts everybody at some more risk."
So far, the Pfizer vaccine seems to offer less defense against infection from the variant, but still good protection from hospitalization, according to an analysis of data from South Africa, where the new variant is driving a surge in infections.
According to the data, a two-dose Pfizer-BioNTech vaccination appeared to provide just 33% protection against infection during South Africa's current omicron wave, but 70% protection against hospitalization, according to the analysis conducted by Discovery Health, South Africa’s largest private health insurer, and the South African Medical Research Council.
Still, the 33% marks a significant drop from the 80% protection against infection afforded during earlier periods.
The researchers say it's encouraging that the study shows that people fully vaccinated with Pfizer have 70% protection against hospital admission during the omicron surge. That's still a drop from the 93% protection seen in South Africa’s delta-driven wave.
The study shows protection against hospital admission even among older age groups, with 67% in people aged 60 to 69 and 60% for people aged 70 to 79.
The analysis was based on examining more than 211,000 positive COVID-19 test results, 41% of which were for adults who had received two doses of the Pfizer vaccine. About 78,000 of the positive results were attributed to omicron infections.
Other studies suggest that both the AstraZeneca and Pfizer vaccines are less effective in preventing symptomatic infections in people exposed to omicron, though preliminary data show that effectiveness appears to rise to between 70% and 75% after a third booster dose.
Dr. Anthony Fauci, the nation’s top infectious disease expert, said Wednesday there is no need, for now, for an omicron-specific booster shot. The two-dose mRNA vaccines, the Pfizer and Moderna shots, still appear to offer considerable protection against hospitalization from omicron, Fauci said.
“If we didn’t have these tools, I would be telling you to be really, really worried,” Fauci said.
Where have omicron cases been reported so far in Illinois?
In Illinois, just two cases of the omicron variant have been confirmed so far - one in Chicago and one in suburban Cook County, but authorities say they are testing for additional cases.
The Cook County Department of Public Health announced the variant was identified in a case Tuesday, but did not specify which suburb the variant was found in.
The case was reported in an asymptomatic person who had received at least two doses of the coronavirus vaccine, officials said.
The person had contact with someone else who tested positive for the omicron variant, but officials would not say whether that contact was in the state of Illinois or out of the state or the country.
Additional cases could soon be identified as "there are other cases that are currently being genotyped for omicron," the Cook County Department of Public Health stated.
"We're investigating positive cases that are also contacts of this case, as well as a couple of other individuals that do not seem to have a direct contact, but these investigations are underway right now," Dr. Rachel Rubin, co-lead and senior medical officer for the Cook County Department of Public Health, said.
In Chicago, the case was reported in a fully vaccinated city resident who had also received a booster dose but was visited by an out-of-state traveler who also tested positive for the variant. The resident did not require hospitalization and had been self-isolating since their symptoms began, officials said.
Arwady also said at the time that test results were pending for city residents who are known contacts of out-of-state or out-of-country omicron variant cases.
"We are following multiple individuals who we know had exposures, whether they were traveling in the U.S. or even internationally, and we have a pretty robust way to share information in a way to protect privacy, but allow us to do case investigation or contact tracing, including over state boundaries," she said.
Where else have cases been reported and where are COVID cases rising?
Globally, more than 75 countries have reported confirmed cases of omicron. In the United States, 36 states have detected the variant. Meanwhile, delta is surging in many places, with hot spots in New England and the upper Midwest. The five states with the highest two-week rolling average of cases per 100,000 people are New Hampshire, Rhode Island, Michigan, Minnesota and Vermont.
Outside the U.S., the president of the European Union said omicron will become the dominant variant in a month and declared that “once again, this Christmas will be overshadowed by the pandemic.”
“The data out of the UK are quite alarming at this point,” and foreshadow what’s to come in the United States, said Bronwyn MacInnis, director of pathogen genomic surveillance at the Broad Institute of MIT and Harvard. For example, she said, by Tuesday afternoon, omicron was already the most common variant in London.
Has anyone died from the omicron variant?
The CDC on Friday said one vaccinated person has been hospitalized with omicron, but no deaths had been reported among the 43 patients that have been followed up on.
Among those patients, 58% were between the ages of 18 and 39 years of age and 79% were fully vaccinated at least 14 days before symptom onset or testing positive.
The CDC reported that 33% of the 43 patients traveled internationally during the 14 days prior to developing symptoms or testing positive, indicating that community spread is underway in the U.S.
According to Reuters, Prime Minister Boris Johnson said Monday that at least one person died in the United Kingdom after contracting the omicron variant, marking what the publication said was the first publicly confirmed death globally from the swiftly spreading strain.
What are the symptoms of omicron?
COVID symptoms linked to the omicron variant have been described as "extremely mild" by the South African doctor who first raised the alarm over the new strain. CDC data showed the most common symptoms so far are cough, fatigue, congestion and a runny nose.
Dr. Angelique Coetzee, chair of the South African Medical Association, told the BBC that she started to see patients around Nov.18 presenting with "unusual symptoms" that differed slightly to those associated with the delta variant, which is the most virulent strain of the virus to date and globally dominant.
"It actually started with a male patient who's around the age of 33 ... and he said to me that he's just [been] extremely tired for the past few days and he's got these body aches and pains with a bit of a headache," she told the BBC.
The patient didn't have a sore throat, she said, but more of a "scratchy throat" but no cough or loss of taste or smell — symptoms that have been associated with previous strains of the coronavirus.
Coetzee said she tested the male patient for COVID, and he was positive, as was his family, and then said she saw more patients that day presenting with the same kinds of symptoms that differed from the delta variant.
Other patients she had seen so far with the omicron variant had also experienced what she described as "extremely mild" symptoms, and she added that her colleagues had noted similar cases.
"What we are seeing clinically in South Africa — and remember I'm at the epicenter of this where I'm practicing — is extremely mild, for us [these are] mild cases. We haven't admitted anyone, I've spoken to other colleagues of mine and they give the same picture."
Here's a complete breakdown of symptoms by variant.
Similarly, in the U.S. case, Fauci said the person was vaccinated but had not received a booster shot and was experiencing “mild symptoms.”
But Moderna CEO Stephane Bancel told CNBC on Monday that omicron symptoms reported in South Africa may not be a good predictor of the variant's virulence in other parts of the world, because the country has a much younger and healthier population than European nations and the United States.
"The trick is you're not going to be able to tell the difference between omicron, delta lambda, plain COVID from the beginning," Landon said. "Influenza or even common rhinovirus causes most of our common colds in the winter. You're not going to know the difference between those if you just look at your symptoms. For many people, those symptoms are overlapping. And while there are some parts of the Venn diagram like taste, loss of taste and smell, or common COVID than these other things, there's a lot of overlap. You're just not going to know especially at the beginning of an illness, what kind of illness you have. You have to get tested."
But getting tested won't necessarily tell you if you have the omicron variant, Landon said.
"When you get a COVID test they're just looking for whether or not you have COVID," she said. "They're not on which kind of in order to figure out the exact strain of COVID. You have to do this thing called sequencing, which takes a lot longer. It's much more intensive. You certainly can't get that back in 24 hours, and it's only done by specialized labs."
Is Chicago taking any precautionary measures in light of the newly detected variant?
Arwady said the city plans to continue pushing for residents to get vaccinated against COVID-19 and get their booster shots as soon as they are eligible, meaning six months after Moderna or Pfizer's vaccine or two months after the Johnson & Johnson vaccine.
"We are still learning. Lots of you are asking, 'Are we going to need an omicron booster?' We might," Arwady said. "We’ll know in another two weeks or so once all the data has been collected related to how well not just has the vaccine been protecting around the world, but has the booster been protecting. How well has 'natural immunity,' been protecting? Because we've been seeing a lot of folks who were kind of counting on prior infection getting infected again with this omicron variant in other parts of the world. And so I don't have the answers out of whether an omicron booster will be needed, but what I do know is that getting the vaccines we have now and getting boosted has helped protect against the spread of omicron in a number of case examples."
Masks will continue to be required indoors, Arwady said, and testing availability will be increased. City employees will be encouraged to stay home if they are sick, though vaccine requirements will likely continue and Chicago may begin requiring proof of vaccination for certain public spaces or activities, Arwady said.
"I'm more interested in that than I am in needing to, you know, do some of the major shutdowns and theaters and many other places have already been doing this but it is certainly something that if, you know, as this increase is continuing and perhaps with the new variant we may do more of."
Does Pfizer's pill to treat COVID work against the omicron variant? What about other treatments?
Pfizer said this week that its experimental pill to treat COVID-19 appears effective against the omicron variant.
The company also said full results of its 2,250-person study confirmed the pill's promising early results against the virus: The drug reduced combined hospitalizations and deaths by about 89% among high-risk adults when taken shortly after initial COVID-19 symptoms.
Separate laboratory testing shows the drug retains its potency against the omicron variant, the company announced, as many experts had predicted. Pfizer tested the antiviral drug against a man-made version of a key protein that omicron uses to reproduce itself.
The Food and Drug Administration is expected to soon rule on whether to authorize Pfizer’s pill and a competing pill from Merck, which was submitted to regulators several weeks earlier. If granted, the pills would be the first COVID-19 treatments that Americans could pickup at a pharmacy and take at home.
Arwady said the early results could be signs of "a really big deal."
"It's not that this pill stops you from getting infected. You are infected with COVID," she said. "You don't get the pill until you're infected with COVID, but you take it early in infection and it works on the enzyme and that in turn, stops the virus from being able to copy itself so much. And it's when we see all of these copies, and it's sort of through your body and it's getting in your lungs, that we tend to see the really serious outcomes. And so one of the reasons I like that approach, going after the the enzyme, is that it we wouldn't expect it to be affected even if the virus continues to mutate."
At the same time, Lemieux said, some monoclonal antibody treatments don’t work as well against omicron in lab tests.