>> reporter: president biden reassuring the nation after a new coronavirus variant set off global alarms. >> i'm sparing no effort and removing all road blocks to keep the american people safe. >> reporter: biden restricting travel from south africa and seven neighboring nations which he warned will slow the spread of omicron but won't stop it. >> here's what it does. it gives us time. gives us time to take more actions to move quicker. >> reporter: the leaders offan can nations calling it an overreach. >> it's outrageous that south africans, southern africa is being punished for having good surveillance. >> reporter: the omicron variant has not yet been detected in the united states but officials say it's only a matter of time. >> sooner or later we'll see cases of this new variant here in the united states. >> reporter: scientists race to determine whether concern over the variant is justified, biden is calling on americans to remain vigilant. >> most americans are fully vaccinated but not yet boosted. if you are 18 years or over, and