(BBC) The World Health Organization (WHO) has declared a new coronavirus variant to be “of concern” and named it Omicron.
It said the variant had a large number of mutations, and early evidence suggested a possible increased risk of reinfection.
It was first reported to the WHO from South Africa on 24 November, and has also been identified in Botswana, Belgium, Hong Kong and Israel.
Several countries banned travel from southern Africa on Thursday.
It is not uncommon for a virus to change, or mutate, over time. A variant becomes a variant of concern when that mutation might affect things like transmissibility, virulence or the effectiveness of vaccines.
In a statement on Friday the WHO said the number of cases of this variant, initially named B.1.1.529, appeared to be increasing in almost all of South Africa’s provinces.
The WHO has said it will take a few weeks to understand the impact of the new variant, as scientists work to determine how transmissible it is.
It has warned against countries hastily imposing travel restrictions, saying they should look to a “risk-based and scientific approach”.
However, the UK, EU countries and Switzerland have temporarily halted flights from some southern African countries.
“It is now important that all of us in Europe act very swiftly, decisively and united,” European Commission chief Ursula von der Leyen said.
South Africa’s Health Minister Joe Phaahla told reporters that the flight bans were “unjustified”.
“The reaction of some of the countries, in terms of imposing travel bans, and such measures, are completely against the norms and standards as guided by the World Health Organization,” he said.
Stock markets across the world also fell sharply on Friday, reflecting the fears of investors over the potential economic impact.