Watch President Biden's remarks on the omicron variant in the player below.
By Kaitlan Collins and Kate Sullivan, CNN
Federal health officials are bracing for the first cases of the new Omicron coronavirus variant to be detected in the US and say there are likely far more cases worldwide than is currently known.
Officials briefed President Joe Biden for approximately 45 minutes Sunday on the new variant, with a heavy dose of caution about what's still unknown. Biden on Monday will provide a public update following a third briefing on the Omicron variant and plans to tell the American people directly what the government does and doesn't know, according to a person familiar with the remarks.
Biden's speech will be more of a reassurance not to panic as scientists evaluate the threat than a specific update on the variant itself. He's expected to push Americans to get vaccinated against Covid-19 and promote booster shots for those who are already full vaccinated.
Biden's team told him it will likely take one to two weeks to know more about the variant, including whether antibodies handle it effectively. The US Centers for Disease Control and Prevention is currently sequencing coronavirus genomes and working closely with state health officials, two steps that will be critical to figuring out if the variant is already in the US.
Biden's chief medical adviser, Dr. Anthony Fauci, said Sunday that hopefully scientists will be able to make a determination soon on whether the Omicron variant is resistant to current Covid-19 vaccines. It's also too soon to tell whether Omicron causes more severe disease.
Fauci said he doesn't think there's any possibility that Omicron could completely evade any protection from the vaccine, but that it may diminish the level of protection.
If there is a diminution of protection, Fauci and other health officials said getting a Covid-19 vaccine booster shot could help enhance protection, since boosters enlarge the capacity of the body to recognize all kinds of mutations on coronavirus variants.
Vaccine maker Moderna's chief medical officer told CNN that the Omicron variant has at least 50 mutations -- including 30 on the key spike protein, which allows the virus to enter human cells, alone. He added that Omicron has thrown a "new wrench" into the fight against Covid-19, but emphasized that having some vaccination will help fight even a very altered and highly dangerous variant.
Biden announced Friday the US would restrict travel from South Africa and seven other countries starting Monday because of the new variant. The Biden administration is now restricting travel from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi. The President was acting on advice from Fauci and the CDC.
The Omicron variant has already been detected on five continents -- North America, Australia, Africa, Europe, Asia -- and the travel restrictions are already generating push back, with South Africa's Ministry of International Relations and Cooperation saying they are "akin to punishing" South Africa.
The Omicron variant was the quickest to be labeled a "variant of concern" by the World Health Organization because of its seemingly fast spread in South Africa and its many troubling mutations.
WHO designates coronavirus variants as either variants of concern -- meaning they look dangerous enough to bear close scrutiny and continual updates -- or as variants of interest, or variants under monitoring. Only five currently meet the definition for variants of concern: Alpha, Beta, Gamma, Delta and Omicron.
This story has been updated with additional information.
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CNN's Ben Tinker and Maggie Fox contributed to this report.