Joe Biden on Monday said the new Omicron variant of the coronavirus was a “cause for concern, not a cause for panic”, as the US implemented restrictions on travel from South Africa and several other countries.

In remarks from the White House, Biden urged all Americans to get vaccinated, including booster shots, saying it was the best protection against the new variant.

He warned that travel restrictions which took effect on Monday would not prevent the spread of the virus in the US. He also said the ban would give public health officials “time to take more actions, to move quicker, to make sure people understand you have to get your vaccine”.

No cases of the variant have yet been identified in the US. Biden said it was only a matter of time.

“Sooner or later, we are going to see new cases of this new variant here in the United States, and we’re going to have to face this new threat, just as we have faced the ones that came before it,” Biden said after meeting his Covid-19 advisers.

Cautioning that there was still much to be learned about the variant, Biden said he was working with vaccine makers to develop “contingency plans” in the “hopefully unlikely” event that updated shots or boosters are needed.

“We do not yet believe that additional measures will be needed,” he said.

He promised to put forward a more detailed strategy on Thursday. “Not with shutdowns or lockdowns,” he said of the forthcoming plan, “but with more widespread vaccinations, boosters, testing and more.”

Answering questions, Biden said lockdowns were not under consideration.

“If people are vaccinated and wear their mask, there’s no need for a lockdown,” Biden said.

Banning travel from other countries recalls the earliest days of the pandemic in 2020, and comes just weeks after the US re-opened its borders to vaccinated travelers from Europe. The new restrictions stop travelers from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini (formerly Swaziland), Mozambique and Malawi coming to the US. The restrictions do not apply to US citizens and lawful permanent residents.

The US is not alone in imposing such restrictions. Many countries have taken similar measures, closing borders and halting travel in a scramble to try to contain the new variant.

Biden spoke after the World Health Organization warned that the global risks posed by Omicron were “very high”, though significant questions remained including whether it is more transmissible, will cause more severe outcomes, or can evade antibodies provided by existing vaccines. Health officials say it appears to be more transmissible but that more analysis is needed.

The variant was identified by researchers in South Africa, and has been detected in the UK, European countries, Canada, Australia and Israel.

Officials in South Africa and other affected nations responded bitterly to the new wave of travel restrictions, saying they were once again bearing the consequences of a failure by wealthier nations to provide vaccines and resources to the continent.

“The objective here is not to punish. It is to protect the American people,” White House press secretary Jen Psaki said.

Biden commended South Africa for its transparency in identifying and reporting the emergence of Omicron, named for the letter in the Greek alphabet.

“This kind of transparency is to be encouraged and applauded because it increases our ability to respond quickly to any new threats and that’s exactly what we did,” the president said.

Asked if travel restrictions might make countries more reluctant to report new variants, Biden defended his administration’s actions.

“We needed time to give people an opportunity to say get that vaccination now,” he said. “It’s going to move around the world. I think it’s almost inevitable that there will be at some point that strain here in the United States.”

Despite widespread vaccine availability, the US inoculation rate remains stubbornly low compared with other western countries. Just 59.1% of the US population is fully vaccinated against the coronavirus, according to the Centers for Disease Control and Prevention. Politicization of public health guidelines and vaccine misinformation have complicated coronavirus response efforts.

Many Republicans have denounced vaccine mandates and mask requirements, even as intensive care units fill up. Yet as infections rise again in some parts of the country, the same conservatives are blaming Biden for failing to contain the pandemic, a central promise of his presidential campaign.

Public confidence in Biden’s handling of the pandemic has tumbled, polls show, dragging down his overall approval ratings.

On Monday, Biden insisted his administration has made substantial progress.

“A year ago, America was floundering,” the president said, contrasting Thanksgiving celebrations this year with those in 2020, when public health officials advised against travel and large gatherings.

By Christmas, Biden said 71% of American adults would be vaccinated, compared with just 1% a year before. Nearly all schools have reopened and children as young as five are eligible to be vaccinated. Early this month, the CDC expanded eligibility for Covid-19 booster shots to all aged 18 and older, if at least six months past a second dose.

Biden acknowledged that Omicron may present new risks.

“Do not wait,” he said. “Go get your booster if it’s time for you to do so. And if you are not vaccinated, now is the time to go get vaccinated and to bring your children to go get vaccinated.”