President Joe Biden on Monday called on unvaccinated and unboosted Americans to get their COVID-19 shots before the new omicron variant spreads in the U.S. He, however, did not order any new mandates such as lockdowns.

In a speech from the White House’s Roosevelt Room, Biden said his administration is preparing for the arrival of the variant in the U.S. “sooner or later.”

“This variant is a cause for concern, not a cause for panic,” he said. “We have the best vaccine in the world, the best medicines, the best scientists, and we're learning more every single day. And we'll fight this variant with scientific and knowledgeable actions and speed, not chaos and confusion.

“A fully vaccinated booster person is the most protected against COVID,” Biden added. “Do not wait. Go get your booster if it's time for you to do so. And if you are not vaccinated, now's the time to get vaccinated, and take your children to be vaccinated.”

The variant was first identified days ago in South Africa and was classified by the World Health Organization on Friday as a variant of concern, the first strain of the coronavirus to receive that designation since the delta variant.

On Friday, Biden instituted new travel restrictions from South Africa and seven other nations that began Monday. Several other nations also implemented similar restrictions in recent days, including the United Kingdom, Australia and Canada.

The variant has already been detected in Britain, Italy, Germany, Belgium, Israel, the Netherlands, Australia and Hong Kong. No cases had been reported in the United States as of Monday, but some health experts suspect it could already be in the country.

Biden said he ordered the travel restrictions to allow more time for the U.S. to get ready for the variant, including more people getting vaccinated. About 80 million Americans ages 5 and older have not yet received a vaccination. 

Biden said he doesn’t anticipate expanding the travel restrictions to other countries, but added that “the degree of spread impacts whether or not there’s a need for any travel restriction.”

Dr. Amesh Adalja, a Senior Scholar at the Johns Hopkins University Center for Health Security, agreed with that assessment, telling Spectrum News that travel restrictions do not have a major impact on the spread of the coronavirus.

"We know that this type of thing is very unlikely to have anything but a marginal impact because an efficiently spreading respiratory virus is going to be everywhere before you even notice it," he told Spectrum News.

He said his top medical adviser, Dr. Anthony Fauci, believes existing vaccines will still offer protection against the variant, but it will take a few weeks before scientists better understand what impact omicron has on the shots’ effectiveness.

The president urged Americans, vaccinated or not, to wear masks indoors in public settings.

Biden also said if updated vaccines are needed to slow omicron, his administration will use every tool, without cutting corners, to accelerate their development and distribution, adding the shots will remain free.

“I'm sparing no effort and removing all roadblocks to keep the American people safe,” he said.

Biden said he will unveil Thursday a detailed strategy for fighting COVID-19 this winter. The plan will focus on “widespread vaccinations, boosters, testing and more,” but not lockdowns, he said.

“If people are vaccinated and wear their masks, there's no need for lockdown,” the president said.

Dr. Adalja told Spectrum News that it's wise of Biden to focus on vaccines and testing instead of lockdowns and other mandates.

"I don't think that we necessarily have to use blunt tools in November of 2021 because we've got so much more now than we did back in March of 2020," Dr. Adalja said.

On Sunday, Biden met with members of his White House COVID Response Team, as well as Fauci. 

Fauci told Biden that it will take about two weeks "to have more definitive information on the transmissibility, severity and other characteristics of the variant.”

"Dr. Fauci also reiterated that boosters for fully vaccinated individuals provide the strongest available protection from COVID," the White House said in a statement. "The COVID Response Team’s immediate recommendation to all vaccinated adults is to get a booster shot as soon as possible; all adults are eligible for a booster if they were vaccinated six months ago or more with Pfizer or Moderna, or two months ago or more with Johnson & Johnson. Importantly, those adults and children who are not yet fully vaccinated should get vaccinated immediately."

On Monday, Fauci reiterated that stance, telling ABC's "Good Morning America" that it could be a week or two before scientists learn how dangerous the variant is compared to previous mutated strains and how well the vaccines stand up to the variant.

Fauci called any speculation about the variant "premature," but said, “It's inevitable that, sooner or later, it's going to spread widely because it has at least the molecular characteristics of being highly transmissible.”

Fauci told "GMA" that omicron has a "transmissibility advantage," but said that "the extent of that, again, still needs to be worked out. We'll know soon."

Dr. Ashish Jha, dean of Brown University's School of Public Health, told NBC's "Today" on Monday that it's "extremely unlikely" omicron will completely evade COVID-19 vaccines.

"I think that our vaccines will hold up," he said. "The question is: Is it a little bit less effective? A lot less effective? We will have that data — both laboratory data and clinical data — in the next week or two at the most."

"If you're fully vaccinated – and especially if you're boosted – you're going to have more protection against this variant," he added.

Dr. Francis Collins, director of the National Institutes of Health, said similar, urging people not to panic, but to get vaccinated and boosted.

"We're going to get better information about this," Collins told CNN about the variant. "There's no reason to panic. But it is a great reason to go get boosted."

While Biden did not announce any new federal mandates Monday, some localities are getting prepared: For instance, New York City health officials recommended indoor mask-wearing Monday to get ahead of the variant.

"We do anticipate detecting the omicron in New York in the coming days, based on what we know about its global spread," NYC Health Commissioner Dr. Dave Chokshi said. "A lot is still unknown about omicron since it is so early, but studies are underway and we will know more about the variant in the coming weeks."

“Everyone knows there's still a lot of information we need, and that will take days or even a few weeks to come in,” Mayor Bill de Blasio said. “But we’re gonna be in a very vigilant state in the meantime and taking any and all actions as we get facts to support them.”

Collins said Sunday that there is no data yet to suggest the new omicron variant causes more serious illness than delta, though its swift spread would indicate that it is highly contagious.

“I do think it’s more contagious [than previous variants] when you look at how rapidly it spread through multiple districts in South Africa,” Collins said on CNN’s "State of the Union.”