While millions of Americans were enjoying Thanksgiving weekend with loved ones, health officials were sounding the alarm on a "heavily mutated" coronavirus variant emerging in South Africa.
The World Health Organization announced Friday it had designated the new strain a "variant of concern" and named it omicron.
Not much is yet known about new variant but experts say it could take hold, causing infections to surge.
"Omicron's very emergence is another reminder that although many of us might think we are done with COVID-19, it is not done with us," said the WHO's director general Tedros Adhanom Ghebreyesus.
Here's everything to know about omicron and why Americans should take notice.
What is omicron?
The World Health Organization designated the B.1.1.529 variant a "variant of concern" Friday and named it omicron after the 15th letter of the Greek alphabet.
WHO uses the Greek alphabet as a variant classification system to simplify understanding and avoid stigmatizing countries where they're first identified.
Omicron, which can be pronounced both ä-mə-ˌkrän or ō-ˈmī-(ˌ)krän, according to Merriam-Webster, was first identified in South Africa last week. The U.S. began restricting travel from South Africa and several other countries Monday due to the latest "variant of concern."
What are the symptoms?
WHO says there's no evidence to suggest that symptoms linked to omicron are different from those caused by other variants.
Dr. Angelique Coetzee, a private practitioner and chair of South African Medical Association, was one of the first doctors in South Africa to detect the new variant.
She told Reuters symptoms of the omicron variant were "very mild" and could be treated at home. These infections were first reported in university students who were younger and tended to have milder disease.
But like all coronavirus variants, WHO said, omicron may be capable of causing severe disease or death, particularly among vulnerable populations.
Symptoms of COVID-19 caused by any known coronavirus variant can include fever or chills, cough, shortness of breath, fatigue, muscle or body aches, headache, sore throat, a loss of taste or smell, sore and congestion or runny nose.
Where has it been detected?
South African scientists say omicron may be behind the recent spike in COVID-19 infections in Gauteng, the country's most populous province.
Portuguese health authorities identified 13 cases of omicron Monday among members of a top soccer club. One of the players who tested positive had recently traveled to South Africa.
Canada's health minister says the country's first two cases of omicron were found in Ontario after two individuals who had recently traveled from Nigeria tested positive.
The variant has also been detected in travelers to Belgium, Botswana, Hong Kong, Australia, and Israel.
Should I be concerned about it?
In a media briefing Monday, President Joe Biden said omicron is "a cause for concern, not a cause for panic."
As of Monday afternoon, the Centers for Disease Control and Prevention said no cases of omicron have been identified in the U.S.
However, health experts believe omicron is likely already spreading undetected.
"Our surveillance in the U.S. is still not what it should be by a long shot," said Julie Swann, professor at North Carolina State University, who studies pandemic modeling and health systems. "It's almost positively in the U.S. but we're not sequencing enough samples and we're not testing enough people."
President Biden: Omicron coronavirus variant 'a cause for concern, not a cause for panic'
Omicron, the newest coronavirus variant: How to pronounce it, how it got its Greek name, and what it means
It's not clear whether infection with omicron causes more severe disease compared to infections with other variants, WHO said. However, preliminary data suggests that there are increasing rates of hospitalization in South Africa.
It's also unclear how well the virus evades immunity from previous infection or COVID-19 vaccines to cause a breakthrough infection.
But even with so little information, health experts say people should be watchful.
"Americans should take this variant seriously," Swann said. "Even if this one turns out to be not as bad as we fear, there will be another one that will."
Are there any deaths linked to omicron?
As of Monday, no deaths were reported associated with the new variant.
What makes omicron different from other variants?
Omicron appears to have about 30 mutations in on the coronavirus' spike protein.
Out of the approximately 30 mutations, 26 are unique to omicron and don't appear in other variants of concern, according to Dr. Venky Soundararajan, co-founder and chief medical officer at nference, a data analytics firm in Massachusetts.
In comparison, the alpha variant has only four unique mutations, beta has six, gamma has eight and delta has seven.
"I'm less concerned about the fact that these mutations exist and I'm more concerned about the fact that we know very little about many of them," Soundararajan said.
A handful of omicron's mutations that exist in other variants have been associated with previous surges of positive COVID-19 cases, he said. Some of these mutations are believed to increase transmissibility while others may help the virus evade immunity.
Most of these mutations are clustered at the ACE2 receptor and antibody binding sites, Soundararajan said, which are also sites targeted by the COVID-19 vaccines and antibodies.
The most intriguing mutation is the ins214EPE insertion, he said. This addition introduces three new amino acids, corresponding to nine nucleotides, to the virus's genetic profile.
However, that doesn't necessarily mean the insertion is more dangerous. A preprint study, not yet peer-reviewed, authored by Soundararajan shows this same insertion is present in seasonal coronaviruses.
This could mean the virus transmits more easily, he said, but it could also mean it causes only mild or asymptomatic disease to evade detection.
"In evolution, when you see a virus pick up a trait, it loses something else. You may see higher transmission but lower odds of hospitalization," Soundararajan said. "That might be the silver lining."
How quickly could it spread?
Scientists say more data is needed to determine severity of illness, but real-world evidence suggests omicron may be highly transmissible.
Dutch health authorities said they detected more than 60 COVID-19 cases among 624 passengers who flew on two flights from South Africa to Amsterdam's airport, Reuters reported, despite requiring a negative test or proof of vaccination.
"The filtration on planes are better, there tend to be mask requirements and most airline companies are requiring a negative test, so I would not have expected this level of positivity so quickly on that flight," Swann said. "I found it a bit worrisome."
Do the COVID-19 vaccines protect against omicron?
Dr. Anthony Fauci, the nation's leading infectious disease expert, told Biden he believes "existing vaccines are likely to provide a degree of protection against severe cases of COVID," reiterating that booster shots on top of full vaccination will provide stronger protection.
However, other scientists say it will likely take weeks to sort out if the new variant is more infectious and if vaccines are still effective against it.
COVID-19 vaccine developers with authorized shots in the U.S. - Pfizer-BioNTech, Moderna and Johnson & Johnson - have all pledged to reformulate their shots to protect against omicron "if needed," which may include an omicron-specific booster.
"It is imperative that we are proactive as the virus evolves," Stéphane Bancel, Chief Executive Officer of Moderna, said in a statement Friday. "The mutations in the omicron variant are concerning and for several days, we have been moving as fast as possible to execute our strategy to address this variant."
What precautions should I take?
Preliminary evidence suggests there may be an increased risk of reinfection with omicron compared to other variants of concern, according to WHO, but more information is needed.
Biden urged the public to get fully vaccinated, and if eligible, to get a COVID-19 booster as soon as possible. Waning immunity in people who received their first shots more than six months ago may put them at risk of breakthrough infection.
The CDC updated its guidance Monday afternoon, recommending that all adults 18 and older should get a booster shot either six months after their initial Pfizer-BioNTech or Moderna vaccine series or two months after their initial J&J vaccine.
"If you are 18 years and over and got fully vaccinated before June 1, go get the booster shot today," Biden said. "They're free and available in 80,000 locations coast to coast. Do not wait."
Anyone who gathered with non-household members over the holiday should consider getting tested for COVID-19, Swann said. She also urged anyone who has traveled away from their community to get tested.
"That would allow us to get a handle on things," she said. "It will continue to spread but slow it down to give us time to know what this is and what does it mean, and be prepared for it."
Americans should also consider wearing masks, regardless of vaccination status, especially around people with compromised immune systems who are more at risk of severe disease, hospitalization and death from COVID-19.
Biden also pushed parents to get their children vaccinated now that the Pfizer-BioNTech vaccine has been authorized for kids 5 to 11.
"Most of our children across America are not fully vaccinated, yet," Swann said. "People who are not fully protected with the full recommended dosage of vaccines should take extra care in gathering with anyone outside their household."
Contributing: Associated Press. Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.
Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.
This article originally appeared on USA TODAY: Omicron variant symptoms, mutations, vaccines: What you need to know