A slew of nations – including Canada – moved to stop air travel from southern Africa, and Israel warned that it was on the “threshold of an emergency” over the weekend as the world reacted to news of a new, potentially more transmissible COVID-19.

A World Health Organization (WHO) panel named the variant “omicron” and classified it as a highly transmissible virus of concern, the same category that includes the predominant delta variant, which is still a scourge driving higher cases of sickness and death in Europe and parts of the United States.

Medical experts, including WHO, warned against any overreaction before all elements were clear but nations who acted said their concerns were justified.

Canada immediately banned the entry of all foreigners who have travelled to southern Africa in the last two weeks. The countries include South Africa, Mozambique, Namibia, Zimbabwe, Botswana, Lesotho and Eswatini.

On Sunday Ontario reported the first two cases of the new COVID-19 variant of concern. Both cases were found in the Ottawa area in people who had recently been in Nigeria.

A statement from the province says it’s ”prepared and ready to respond to this new variant.”

The federal health minister says authorities are continuing to assess the situation, but says this should not be cause for alarm. Jean-Yves Duclos also says the development “demonstrates that our monitoring system is working.”

Australia and Austria on Sunday became the latest countries to detect the virus variant in travellers who arrived from southern Africa, while Israel decided to bar entry to all foreign nationals – the toughest of a growing raft of curbs imposed by nations around the world as they scramble to slow its spread.

Confirmed or suspected cases of the new variant had already emerged in several European countries, in Israel and in Hong Kong, just days after it was identified by researchers in South Africa. The “act first, ask questions later” approach reflected growing alarm about the emergence of a potentially more contagious variant nearly two years into a pandemic that has killed more than 5 million people, upended lives and disrupted economies across the globe.

“The last thing we need is to bring in a new variant that will cause even more problems,” said German Health Minister Jens Spahn, amid a massive spike in cases in the 27-nation European Union. A German state official said that there’s a “very high probability” that the omicron variant had already arrived in the country. French officials suspected the same.

British Health Secretary Sajid Javid told lawmakers, “Early indications show this variant may be more transmissible than the delta variant and current vaccines may be less effective against it. We must move quickly and at the earliest possible moment.”

The UK immediately announced that it was banning flights from South Africa and five other southern African countries and after reporting two cases on Saturday, British Prime Minister Boris Johnson said that anyone arriving in England will be asked to take a mandatory PCR test for COVID-19 on the second day and must self isolate until they provide a negative test. If someone tests positive for the omicron variant, their close contacts will have to self-isolate for 10 days regardless of their vaccination status.

Johnson also said mask-wearing in shops and on public transport will be required and that the vaccination program will be accelerated.

Spain announced it won’t admit unvaccinated British visitors starting Dec. 1.

Belgium was the first European Union country to announce a case of the variant on Friday; on Sunday the Netherlands reported 13 cases. They were among 61 people who tested positive for the virus after arriving on the last two flights to Amsterdam’s Schiphol airport before a flight ban was implemented. They were immediately put into isolation, most at a nearby hotel, while sequencing was carried out.

Israel, one of the world’s most vaccinated countries, announced that it had also detected the country’s first case of the new variant, in a traveller who returned from Malawi, prompting Prime Minister Naftali Bennett to declare on Friday that the nation is “on the threshold of an emergency situation.”

The World Health Organization cautioned not to jump to conclusions too fast with Dr. Michael Ryan, the head of emergencies at the WHO, stating that “it’s really important that there are no knee-jerk responses.”

“We’ve seen in the past, the minute there’s any kind of mention of any kind of variation and everyone is closing borders and restricting travel. It’s really important that we remain open, and stay focused,” he said.

Those urgings quickly fell on deaf ears.

EU Commission President Ursula von der Leyen said flights will have to be suspended “until we have a clear understanding about the danger posed by this new variant, and travellers returning from this region should respect strict quarantine rules.” She also warned that “mutations could lead to the emergence and spread of even more concerning variants of the virus that could spread worldwide within a few months.”

Germany said airlines coming back from South Africa will only be able to transport German citizens home, and travellers will need to go into quarantine for 14 days whether they are vaccinated or not.

Italy’s health ministry also announced measures to ban entry into Italy of anyone who has been in seven southern African nations in the past 14 days due to the new variant. Other countries are planning similar measures.

The Japanese government announced that Japanese nationals travelling from Eswatini, Zimbabwe, Namibia, Botswana, South Africa, and Lesotho will have to quarantine at government-dedicated accommodation for 10 days and do a COVID test on Days 3, 6 and 10. Japan has not yet opened up to foreign nationals.

The US and Russian also banned flights from the region, as did a growing list of countries that included Brazil, Iran, New Zealand, Thailand, Indonesia, Singapore, Sri Lanka, the Maldives, and Saudi Arabia.

The South African government addressed the British ban, stating the decision “seems to have been rushed as even the World Health Organization is yet to advise on the next steps.”

But UK health minister Javid warned, “This is a real reminder that this pandemic is far from over.”