The newly discovered omicron variant has been labeled a "variant of concern" by the World Health Organization (WHO) and has led to a wave of urgent travel restrictions worldwide. But experts say the variant's consequences for public health ultimately will depend upon the still-unknown answers to three key questions.

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Omicron is named a 'variant of concern'

On Thursday, scientists in South Africa announced the discovery of a new coronavirus variant, B.1.1.529, after a steep rise in Covid-19 cases in the country over the past few weeks.

"This variant has a large number of mutations, some of which are concerning," WHO said. "Preliminary evidence suggests an increased risk of reinfection with this variant, as compared to other [variants of concern]."

In response, several countries, including the United Kingdom, the United States, and Israel, have enacted travel restrictions for several southern African nations. So far, the omicron variant has been detected in more than a dozen countries, including Australia, Canada, Hong Kong, the U.K., and the Netherlands.

The 3 big unanswered questions about omicron

Several experts—including Ashish Jha, dean of the Brown University School of Public Health, and Leana Wen, a professor of health policy and management at George Washington University—said that the ultimate consequences of the omicron variant will depend on three variables:

• How transmissible is it? That is, does it spread as rapidly between individuals as the highly contagious delta variant—or even faster?

• How virulent is it? That is, does it cause severe illnesses, such as those that ultimately lead to hospitalization or death?

• Does it evade the immune system's existing defenses? That is, is the omicron variant especially likely to infect people who have preexisting immunity to other coronavirus variants, either due to immunization or natural infection?

Although experts emphasize that much about the omicron variant remains unknown, early data is beginning to shed light on these key questions. Here's what the data suggests so far, and what experts say the variant's mutations suggest about its likely capabilities.

1. How transmissible is the omicron variant?

Since its discovery, the omicron variant has quickly become the predominant coronavirus variant in South Africa, where it now accounts for the majority of the new cases in the country.

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It's unclear, however, whether that rapid rise means that the omicron variant is especially transmissible. An alternative explanation is that omicron happened to spread in a few "superspreader" events at a time when other variants have been fading in South Africa, meaning that its apparently rapid spread is just a statistical fluke.

But several experts said it is likely that the omicron variant is highly transmissible since it carries mutations similar to those found on the very contagious delta variant, as well as other mutations hypothesized to increase transmissibility.

Aris Katzourakis, an evolutionary biologist at the University of Oxford, said that although it is difficult to determine a virus's transmissibility by its mutations alone, "if we were looking out for mutations that do affect transmissibility, [the omicron variant has] got all of them."

2. How virulent is the omicron variant?

Currently, it is not known whether the omicron variant causes more severe disease than other coronavirus variants—and experts say early data gives reason both for hope and for concern.

On the hopeful side, reports suggest that most people infected with the variant so far have experienced mild symptoms.

Angelique Coetzee, chair of the South African Medical Association who first alerted authorities to patients with the omicron variant, said infected patients had symptoms that were different from those seen with the delta variant, but that they were "very mild."

"Most of them are seeing very, very mild symptoms and none of them so far have admitted patients to surgeries," Coetzee said. "We have been able to treat these patients conservatively at home."

According to Coetzee, the most common complaints among patients infected with the omicron variant have been severe fatigue, headaches, body aches, and pain. So far, patients have not reported a loss of smell or taste or a major drop of oxygen.

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However, Coetzee noted that many of the patients she has seen have been relatively young and healthy and that the omicron variant may lead to severe disease in older people, especially those with comorbidities.

"What we have to worry about now is that when older, unvaccinated people are infected with the new variant, and if they are not vaccinated, we are going to see many people with a severe [form of the] disease," she said.

Additionally, hospitalizations and deaths tend to lag coronavirus infections by several weeks. As such, it's possible that patients with the omicron variant simply haven't had time to deteriorate but that more serious complications will emerge in the weeks to come.

For its part, WHO says "[t]here is currently no information to suggest that symptoms associated with omicron are different from those from other variants."

3. Can the omicron variant evade the immune system's existing defenses?

According to several experts, some of the omicron variant's mutations suggest it can evade some of defenses the body erects against the coronavirus after immunization or infection. It's unclear, however, whether that will translate into a real-world reduction in vaccine effectiveness.

"There are many [mutations in the omicron variant] we've never studied before, but just looking at the location on the spike, they are in regions that we know are immuno-dominant," said Penny Moore, a virologist at the National Institute for Communicable Diseases in South Africa.

Separately, Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center, said, "Based on lots of work people have done on other variants and other mutations, we can be pretty confident these mutations are going to cause an appreciable drop in antibody neutralization."

Scientists around the world are currently testing the omicron variant against the antibodies generated by current Covid-19 vaccines. According to the New York Times, vaccine manufacturers, such as Moderna and Pfizer-BioNTech, are also preparing to potentially adjust their vaccine formulas to enhance protection as needed.

Jerica Pitts, a Pfizer spokesperson, said that the company's scientists "can adapt the current vaccine within six weeks and ship initial batches within 100 days in the event of an escape variant" that can evade immunity.

Still, while experts say it's important to prepare for potentially severe effects from the omicron variant, they emphasized that existing medications and defenses should still provide meaningful protection. Writing on Twitter, Jha said that "this is not a reset to March of last year—the world has the means to manage this variant. Let's use them." (Corder et al., Associated Press, 11/29; Steinhauser et al., Wall Street Journal, 11/28; Nebehay/Winning, Reuters, 11/26; Faust, Inside Medicine, 11/26; Jha, New York Times, 11/27; Kupferschmidt, Science, 11/27; Mandavilli, New York Times, 11/27; Reuters, 11/28; Thornycroft/Brown, The Telegraph, 11/27; Mandavilli, New York Times, 11/28; Mukherjee, Reuters, 11/28)