The Omicron variant upends the global pandemic response.
Britain, Israel and others announced new restrictions as some health experts urged caution.,
Governments around the world reintroduced restrictive measures as scientists raced to study a new coronavirus variant and several cases were spotted in Europe days after it was first detected in southern Africa.
Omicron, a new variant first detected in Botswana, sent Europe into high alert after cases were detected in the United Kingdom, Germany, Italy and Belgium. The Czech Republic, Austria, Israel and the Netherlands were all investigating suspected cases of the variant.
Relatively little is known about Omicron. It has mutations that scientists fear could make it more infectious and less susceptible to vaccines — though neither of these effects is yet to be established. Most confirmed cases of the variant are contained to southern African countries, but there are worries the virus could have spread more widely before scientists there discovered it.
“There’s been a window of probably about two weeks conservatively that this virus has been spreading,” Andrew Pekosz, an epidemiologist from Johns Hopkins Bloomberg School of Public Health said in an interview on Saturday. It is likely the variant is already in New York, he said.
“There certainly is a chance that it has already spread globally, but we just don’t know yet,” Mr. Pekosz added.
European leaders, already struggling with a surge in Covid-19 cases that has made it once again the epicenter of the pandemic, tried to strike a balance between increasing caution and avoiding panic.
Sixty-one passengers out of more than 500 on two flights from southern African countries into the Netherlands on Saturday tested positive for the coronavirus and are quarantining in Amsterdam. The Omicron variant is likely to be found in some of those 61 passengers who tested positive, the Dutch authorities said.
The European Union is restricting travel to and from seven countries in southern Africa, Botswana, Eswatini, Lesotho, Mozambique, Namibia, South Africa and Zimbabwe, while the United States and South Korea have targeted those countries and Malawi. Britain initially restricted travel from those eight nations before adding Angola, Malawi, Mozambique and Zambia to its red list.
Canada, Australia, Russia, Thailand, Sri Lanka, Singapore, Saudi Arabia, Oman and Morocco have all announced similar restrictions.
Israel said Saturday it would close its borders to foreign nationals for two weeks.
In a news conference on Saturday evening, Prime Minister Boris Johnson said that to curb the spread of the variant, face masks would be required in stores and on public transportation, a rule the country had ended in July.
Britain will also require travelers from abroad to get a PCR test within 48 hours of their arrival and require contacts of those who test positive with a suspected case of Omicron to self-isolate for 10 days, regardless of vaccination status.
The variant was also detected in Hong Kong, which prompted “the most stringent boarding and quarantine requirements” for travelers coming from southern African countries.
“I think certainly caution is warranted to restrict travel and to watch this closely, but at the end of the day, we really need a lot more data to evaluate this new variant,” Philip A. Chan, an infectious disease doctor at Brown University who has helped lead the Covid-19 response for Rhode Island, said.
What we do know, he said, is that the Omicron variant seems to be overtaking the Delta variant in southern African countries, which suggest Omicron is more contagious and that it can overcome some of the natural immunity and vaccine immunity.
“Neither one of those things are good, obviously. And I think that those are the two reasons that have experts and scientists so concerned,” Dr. Chan said. But he still “urges caution and patience.”
“Let’s wait to see what the data shows. Let’s take appropriate precautions,” he said.
Dr. Chan also cautioned that without a robust global vaccination effort, “we are half-treating the pandemic” and leaving the world open to new and more transmittable variants.