The discovery of a new coronavirus variant has sent a chill through much of the world as nations raced to halt air travel, markets fell sharply and scientists held emergency meetings to weigh the exact risks.
The World Health Organisation has named the B.1.1.529 Covid variant "Omicron" and an advisory group has said it should be designated as "of concern".
In a statement, the WHO said preliminary evidence suggests the latest variant carries a "higher risk of re-infection than other variants of concern".
The statement said the first known confirmed B.1.1.529 infection was from a specimen collected on November 9, 2021.
"This variant has a large number of mutations, some of which are concerning.
"Preliminary evidence suggests an increased risk of reinfection with this variant, as compared to other VOCs [variants of concern]. The number of cases of this variant appears to be increasing in almost all provinces in South Africa."
Medical experts have warned against any overreaction before the variant that originated in southern Africa was better understood. But a jittery world feared the worst nearly two years after Covid-19 emerged and triggered a pandemic that has killed more than 5 million people around the globe.
The US said it will ban travel from South Africa and seven other African nations by non-US citizens beginning Monday. European Union nations agreed earlier in the day to impose a ban on travel from southern Africa to counter the variant's spread. The U.K., Canada and other countries have imposed similar restrictions.
The moves have renewed a debate over whether flight bans and other travel restrictions work to prevent the spread of new variants. Some say at best the restrictions can buy time for new public health measures to be put in place. At worst, they do little to stop the spread and give a false sense of security.
The Africa Centres for Disease Control and Prevention said it strongly discouraged imposing travel bans on people coming from countries where the variant was reported.
British Health Secretary Sajid Javid told lawmakers the newest variant might be more transmissible than the Delta variant and render vaccines less effective.
"We must move quickly and at the earliest possible moment," Javid said.
There was no immediate indication that the variant causes more severe disease. As with other variants, some infected people display no symptoms, South African experts said.
Even though some of the genetic changes appear worrisome, it was unclear if the new variant would pose a significant public health threat. Some previous variants, like the Beta variant, initially concerned scientists but did not spread very far.
Some nations moved to stop air travel from southern Africa, and stocks tumbled in Asia, Europe and the United States. The Dow Jones Industrial Average dropped more than 1000 points. The S&P 500 index was down 2.3 per cent, on pace for its worst day since February. The price of oil plunged nearly 12 per cent.
"The last thing we need is to bring in a new variant that will cause even more problems," German Health Minister Jens Spahn said amid a massive spike in cases in the 27-nation European Union, which recommended a ban on flights from southern African nations.
EU Commission President Ursula von der Leyen said flights "should 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 insisted on extreme caution, warning 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."
Belgium became the first European Union country to announce a case of the variant. It involved a person who came from abroad.
"It's a suspicious variant. We don't know if it's a very dangerous variant," Health Minister Frank Vandenbroucke said.
Showing how complicated the spread of a variant can be, the traveller returned to Belgium from Egypt on November 11 and became sick on Monday with mild symptoms, according to professor Marc Van Ranst, who works for the scientific group overseeing the Belgian government's Covid -19 response.
Israel, one of the world's most vaccinated countries, announced on Friday it also detected the country's first case of the new variant in a traveller who returned from Malawi. The traveller and two other suspected cases were placed in isolation. Israel said all three were vaccinated, but officials were looking into the travellers' exact vaccination status.
After a 10-hour overnight trip, passengers aboard KLM Flight 598 from Capetown, South Africa, to Amsterdam were held on the edge of the runway on Friday morning at Schiphol airport for four hours pending special testing because of the new variant. Passengers aboard a flight from Johannesburg were also being isolated and tested.
"It's ridiculous. If we didn't catch the dreaded bugger before, we're catching it now," said passenger Francesca de' Medici, a Rome-based art consultant who was on the flight.
Some experts said the variant's emergence illustrated how rich countries' hoarding of vaccines threatens to prolong the pandemic.
Fewer than 6 per cent of people in Africa have been fully immunised against Covid -19, and millions of health workers and vulnerable populations have yet to receive a single dose. Those conditions can speed up spread of the virus, offering more opportunities for it to evolve into a dangerous variant.
"This is one of the consequences of the inequity in vaccine rollouts and why the grabbing of surplus vaccines by richer countries will inevitably rebound on us all at some point," said Michael Head, a senior research fellow in global health at Britain's University of Southampton. He urged the Group of 20 leaders "to go beyond vague promises and actually deliver on their commitments to share doses".
The new variant added to investor anxiety that months of progress containing Covid -19 could be reversed.
"Investors are likely to shoot first and ask questions later until more is known," said Jeffrey Halley of foreign exchange broker Oanda.
In a sign of how concerned Wall Street has become, the market's so-called fear gauge, known as the VIX, jumped 48 per cent to a reading of 26.91. That's its highest reading since January, before vaccines were widely distributed.
Speaking before the EU announcement, Dr Michael Ryan, the head of emergencies at the WHO, warned against "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," Ryan said.
The Africa Centres for Disease Control and Prevention agreed and strongly discouraged any travel bans on countries that reported the new variant. It said past experience shows that such travel bans have "not yielded a meaningful outcome".
The UK banned flights from South Africa and five other southern African countries at noon on Friday and announced that anyone who had recently arrived from those countries would be asked to take a coronavirus test.
Germany said its flight ban could be enacted as soon as Friday night. Spahn said flights returning 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.
Germany has seen record daily case numbers in recent days and on Thursday surpassed 100,000 deaths from Covid -19.
Italy's health ministry announced measures to ban entry for anyone who has been in seven southern African nations — South Africa, Lesotho, Botswana, Zimbabwe, Mozambique, Namibia and Eswatini — in the past 14 days due. The Netherlands and the Czech Republic planned 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 accommodations for 10 days and take Covid -19 tests on the third, sixth and 10th days. Japan has not yet opened up to foreign nationals.
The South African government said the UK's decision to temporarily ban South Africans from entering "seems to have been rushed", citing the fact that the WHO has yet to recommend next steps.
The coronavirus evolves as it spreads and many new variants, including those with potentially risky mutations, often die out. Scientists monitor for possible changes that could be more transmissible or deadlier, but sorting out the exact dangers takes time.
The WHO's technical working group was to meet on Friday to assess the new variant — currently identified as B.1.1.529 — and may decide whether to give it a name from the Greek alphabet. It says coronavirus infections jumped 11 per cent in the past week in Europe, the only region in the world where Covid -19 continues to rise.
The WHO's Europe director, Dr Hans Kluge, warned that without urgent measures, the continent could see another 700,000 deaths by the spring.