New York, Nov 30 : US President Joe Biden has sought to reassure the country about the new Omicron variant of the coronavirus, telling Americans that his administration was working with vaccine manufacturers to modify vaccines and booster shots should that prove necessary. "We're throwing everything we have at this virus, tracking it from every angle," Biden said in a White House news briefing on Monday, adding that "I'm sparing no effort, removing all roadblocks to keep the American people safe." "Sooner or later, we're going to see cases of this new variant in the US," he said. "This variant is a cause for concern, not a cause for panic." The President's remarks came as travel restrictions he had announced on Friday were to take effect for non-citizens entering the US from South Africa, where the Omicron variant was first detected, as well as the African countries of Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi, Xinhua news agency reported. Though it remains unclear how effective the vaccines developed by Pfizer, Moderna and Johnson & Johnson, and authorised in the US will be against the Omicron variant, Biden added that the vaccines remain the best protection, urging everyone aged five years and older to get the jabs, and those aging 18 years and older to get an additional booster dose. The vaccines remain free and are authorised for people aged five and above in the US. Boosters are available for all adults who are 18 years and older, either six months after their last Pfizer or Moderna shot or two months after their Johnson & Johnson shot. The booster does not have to be the same brand as the initial vaccination. During the briefing, the President also said that while it will "be a few weeks" before it becomes clear how well the vaccines protect against the new variant, "in the event updated vaccinations or boosters are needed against the new variant, we will accelerate their development with every tool." The World Health Organization warned on Monday that global risks posed by the new Omicron variant of the coronavirus were "very high," despite significant questions about the variant itself. Still, countries around the world rushed to defend against its spread, with a cascade of border closures and travel restrictions that recalled the earliest days of the pandemic. /IANS