First identified in Botswana and South Africa in November, the Omicron variant has surged around the world over the past few weeks, faster than any previously known form of the coronavirus. While there’s a lot that scientists have yet to understand about Omicron, the variant is already causing a rise in new cases that may push some hospital systems to the breaking point.

Scientists first recognized Omicron thanks to its distinctive combination of more than 50 mutations. Some of them were carried by earlier variants such as Alpha and Beta, and previous experiments had demonstrated that they could enable a coronavirus to spread quickly. Other mutations were known to help coronaviruses evade antibodies produced by vaccines.

Based on those mutations, along with a worrying rise in Omicron cases in South Africa, the World Health Organization designated Omicron a “variant of concern” on Nov. 26, warning that the global risks posed by it were “very high.” Since then, the variant has been identified in more than 110 countries. At the beginning of December, a California resident who returned home from South Africa was identified as the first American infected with Omicron. By Dec. 25, the Centers for Disease Control estimated that it made up 58 percent of all new infections in the United States. Omicron is quickly surging to dominance in many parts of the world, living up to the potential that scientists recognized when it was first discovered.

Tracking Omicron and Other Coronavirus Variants

See which countries have reported cases of the Omicron variant.

Yes. It is two to three times as likely to spread as Delta.

The earliest evidence for Omicron’s swift spread came from South Africa, where Omicron rapidly grew to dominance in one province after another. In other countries, researchers have been able to catch Omicron earlier in its upswing, and the picture is the same: Omicron cases are doubling every two to four days — a much faster rate than Delta. For a closer look at how well Omicron spreads, British researchers also observed what happened in the households of 121 people who had been infected with the variant. They found that Omicron was 3.2 times as likely to cause a household infection as Delta was.

Scientists don’t yet know what makes Omicron so good at spreading, but a few clues have emerged from preliminary research. A team of British scientists found that Omicron is particularly good at infecting cells in the nose, for example. When people breathe out through their noses, they can release new viruses. Omicron is also adept at dodging antibodies produced by vaccines and previous infections.

Some symptom differences have emerged from preliminary data. For instance, one possible difference is that Omicron may be less likely than earlier variants to cause a loss of taste and smell.

Data released last week from South Africa’s largest private health insurer, for instance, suggest that South Africans with Omicron often develop a scratchy or sore throat along with nasal congestion, a dry cough and muscle pain, especially low back pain.

But these are all symptoms of Delta and of the original coronavirus, too. It’s likely that the symptoms of Omicron will resemble Delta’s more than they differ.

“There’s probably a huge amount of overlap between Omicron and the prior variants, because they are essentially doing the same thing,” said Dr. Otto O. Yang, an infectious disease physician at the University of California, Los Angeles. “If there are differences, they’re probably fairly subtle.”