The discovery of a new coronavirus variant named Omicron triggered global alarm on Friday as countries tried to suspend travel from southern Africa and stock markets on both sides of the Atlantic coast suffered their biggest falls in more than a year.
The World Health Organisation said Omicron may spread more quickly than other forms, and preliminary evidence suggests there is an increased risk of re-infection.
Travel curtails may be too late to stop Omicron from circulating worldwide, according to epidemiologists. The new mutations were first discovered in South Africa and have been detected in Belgium, Botswana, Israel and Hong Kong.
The United States will restrict travel from South Africa and neighbouring countries on Monday, a senior Biden administration official said.
It could take weeks for scientists to fully understand the variant's mutations and whether existing vaccines and treatments are effective against it. Omicron is the fifth variant of concern designated by the WHO.
The UK Health Security Agency said the variant has a spike protein that is dramatically different from the one in the original coronaviruses that vaccines are based on, raising fears that current vaccines will fare well.
This new variant of the COVID 19 virus is very worrying. Lawrence Young, a virologist at the Britain's University of Warwick, said it was the most heavily mutated version of the virus we've seen to date.
Some of the mutations that are similar to changes we've seen in other variants of concern are associated with enhanced transmissibility and partial resistance to immunity induced by vaccination or natural infection. Those worries raped financial markets, especially stocks of airlines and others in the travel sector, and oil, which fell by about $10 a barrel.
European stocks had their worst day in 17 months, despite the fact that it was 5%, its worst day since October 2020.
Cruise operators Carnival Corp, Royal Caribbean Cruises and Norwegian Cruise Line plunged more than 10% each, while shares in American Airlines, Delta Air Lines and American Airlines fell almost as much.
Several other countries, including India, Japan, Israel, Turkey, Switzerland and the United Arab Emirates, have tightened travel restrictions.
In Geneva, the WHO - experts discussed Friday the risks presented by the variant called B. 529 - had warned against travel curbs for now.
The WHO's emergencies director Mike Ryan praised South Africa's public health institutions for picking up the new variant of the coronaviruses that causes COVID - 19 and said it was important that there were no knee-jerk responses.
Richard Lessells, a South Africa-based infectious disease expert, said that the focus should be on getting more people vaccinated in places that have struggled to access enough shots, and expressed frustration at travel bans.
This is why we talked about the risk of vaccine apartheid. He told Reuters that the virus can develop in the absence of adequate levels of vaccination.
According to medical and human rights groups, less than 7% of people in low-income countries have received their first COVID 19 shot. Many developed nations are giving third-dose boosters.
The news of Omricon is an urgent reminder of why we need to do more to vaccinate the world. The coronavirus has swept the world in the past two years since it was first identified in central China, infecting 260 million people and killing 5.4 million people.
One epidemiologist in Hong Kong said it may be too late to tighten travel curbs against the latest variant.
This virus is most likely already in other places. Ben Cowling, professor of the University of Hong Kong said if we shut the door now, it's going to be too late.
The discovery of a new variant comes as Europe and the United States enter winter, with more people gathering indoors in the run up to Christmas, providing a breeding ground for infection.
Friday marked the beginning of the holiday shopping period in the United States, but stores were less crowded than in years past.
On Black Friday, a real estate agent, Kelsey Hupp, 36, was at Macy's department store in downtown Chicago.
Chicago is masked and vaccinated. She said that I'm not too concerned about it because I got my booster.