The omicron variant is surging. Here’s what we’ve learned so far

With omicron spreading globally at a dizzying pace, scientists are scrambling to learn as much as they can about the latest worrisome variant of the coronavirus. First spotted in South Africa and Botswana at the end of November, omicron is already poised to soon become the dominant variant — dethroning delta — in some regions, public health officials warn. In a few places, it already has. So answers, including how sick does omicron make people and how well do vaccines hobble it, can’t come fast enough.
A rising tide of data on omicron is beginning to provide a glimpse at what’s ahead as we enter year three of the global pandemic, though many questions linger. And with many people preparing to gather with family and friends for holidays, experts are bracing for yet more case surges, compounded by already high infection rates in some countries linked to the still-prevalent delta variant.
Omicron’s collision with the holidays and travel is “a perfect storm,” Thomas Denny, a vaccine expert at Duke University, said December 16 in a call with journalists. At this point, even vaccinated people should be taking precautions, such as wearing masks indoors and testing before family gatherings, he said. “This new variant has thrown us a curve ball at the worst possible time.”
Still, amid the worries, there are positive signals that vaccines can still protect people from the worst of COVID-19. As many countries hurtle toward a season of omicron, here’s what researchers are learning so far.

Omicron’s high number of mutations in important viral proteins, and signs that the variant was behind a surge of COVID-19 cases in South Africa, quickly raised red flags, hurling the pandemic into yet another tsunami of uncertainty (SN: 12/1/21).
In the weeks since omicron emerged, the variant has been identified in more than 85 countries. Some, like Denmark, have identified some cases that date before South African researchers revealed omicron’s presence to the world — a hint that the variant had already slipped across borders from wherever it originated before its November discovery. In many of these places, omicron infections are rising fast.
Omicron is responsible for nearly all new COVID-19 cases in South Africa, and is already the predominant version of the coronavirus in London. The European Centre for Disease Prevention and Control estimates that omicron will be the most common variant across the European Union by mid-January.
In the United States, omicron now appears to reign. The variant was responsible for an estimated 73.2 percent of new infections across the country for the week ending December 18, according to the U.S. Centers for Disease Control and Prevention’s predictions. That’s up from an estimated 12.6 percent the previous week and 0.7 percent the week ending December 4. Omicron now accounts for an estimated 92 percent of new cases in New York and New Jersey and 96.3 percent in Washington, Oregon and Idaho.
Previous data suggested that estimates of omicron’s prevalence from earlier in December were lower. It takes time to collect and analyze viruses from patient samples, Bronwyn MacInnis, director of pathogen surveillance at the Broad Institute of MIT and Harvard, said in a December 14 call with journalists. So the numbers can “change quickly as more data comes in off machines in real time.”
With that in mind, omicron is likely to worsen the surge that is unfolding across the United States. Some places, including New York City, are already seeing large spikes in COVID-19 cases with numbers rising fast. It currently takes about two days for the number of omicron cases to double, CDC director Rochelle Walensky said December 15 in a White House news briefing. Highly infectious delta, in comparison, doubled every two weeks at the beginning of its surge in the United States (SN: 7/2/21).
It was a huge question whether omicron would compete with delta for global dominance. Now, some real-world studies show that omicron is coming on strong in many regions. Preliminary data from the United Kingdom show that omicron is around 3.2 times as likely to spread among households as delta is, researchers with Public Health England, a U.K. health agency, reported December 9.
And people exposed to omicron may get sick faster — and therefore be able to spread the virus sooner — than people exposed to other variants. An analysis of an omicron outbreak at a company Christmas party in Norway found that the median time that a person exposed at the party developed symptoms was three days, researchers reported December 16 in Eurosurveillance. It takes slightly longer for delta infections to cause symptoms — around four days — and about five days for non-delta variants.
The reasons behind omicron’s swift spread are still fuzzy. It could be because omicron is more transmissible than delta or because it can dodge parts of the immune response. Or, more likely, it could be a mixture of both, says Kartik Chandran, a virologist at Albert Einstein College of Medicine in New York City. Some preliminary studies done in lab-grown cells hint that omicron may turn out to be more transmissible than delta, though how much more is unclear. One reason may be because the new variant might make more copies of itself inside host cells than other variants do.
Omicron may also replicate particularly well in bronchial cells — which line the tubes that deliver air to the lungs — compared with how well it grows in lung tissue, researchers reported December 15 in preliminary data from the University of Hong Kong. If the virus is growing well in bronchial cells, symptoms like coughing could release a lot of viruses into the air.
The Hong Kong results may be a sign that omicron might be less likely than variants like delta to invade the lungs of infected people and cause severe illness, but that’s far from definitive. “I don’t think you can really say that the virus is going to be less virulent based on that data alone,” Chandran says. “We’re going to have to wait and see what happens to people.”
There are some hopeful hints from South Africa that omicron might cause less severe disease than what delta causes. But experts caution that it’s far too early to make solid conclusions.
"We should not be lulled into any type of complacency,” Ryan Noach, CEO of Discovery Health, a health insurance provider based in South Africa, said December 14 in a news conference.
The optimism comes because hospitalizations in South Africa aren’t rising as fast as they did in previous surges. What’s more, anecdotal reports from the country suggest that fewer hospitalized patients in the current wave rely on medical interventions to breathe, such as supplemental oxygen.
That information, however, comes with a massive caveat: More than 70 percent of people there have been exposed to the coronavirus in the last 18 months, Noach said. Protection provided by previous infections, or vaccinations, could be the reason people there tend to have milder symptoms.
Experts need to see what happens in other parts of the world before concluding that omicron is a less virulent virus than other variants, Glenda Gray, president and CEO of the South African Medical Research Council, said at the December 14 news conference. Monitoring the severity of COVID-19 cases in places with low vaccination rates and low infection rates will be particularly informative, she said.
A study from the United Kingdom found that so far there is no indication that omicron might cause milder, or more severe, COVID-19 than delta, researchers report December 17. Data on hospitalizations there, however, are still limited.
Even if omicron is ultimately linked to milder disease, that doesn’t mean it isn’t dangerous. More infections overall mean more hospitalizations and more deaths, even if the severe outcomes are a smaller proportion of overall omicron cases than with delta.
In the United States, where delta dominated until recently, the two variants are colliding — and that’s raising fears of this latest wave turning into a tsunami in some places.
“Our delta surge is ongoing and, in fact, accelerating,” Jacob Lemieux, an infectious diseases physician at Massachusetts General Hospital and Harvard Medical School in Boston, said in a December 14 call with reporters. “On top of that, we’re going to add an omicron surge. That’s alarming because our hospitals are already filling up. Staff are fatigued. We’re almost two years into the pandemic, and there may be limits on capacity to handle the kinds of caseloads that we see from an omicron wave superimposed on a delta surge.”

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