The Omicron variant of Covid-19 has been identified in west Africa and the Gulf, as the US said it was further tightening its border controls.
Washington’s announcement was made as more countries reported their first cases of the variant, suggesting it is spreading around the globe.
With Ghana, Nigeria, Norway, Saudi Arabia and South Korea among the latest states to record cases, Omicron has been identified in 24 countries.
Dozens of countries have imposed stricter travel rules, and the US Centers for Disease Control and Prevention (CDC) said on Wednesday it was requiring all air travellers entering the country to show a negative Covid-19 test performed within one day of departure.
Fifty-six countries were reportedly implementing travel measures to guard against Omicron despite warnings by the World Health Organization that “introducing blunt, blanket measures … will only worsen inequities”.
However, a report on Wednesday suggesting that retrospective analysis in Nigeria had found evidence of Omicron as early as October – raising fears it had been circulating weeks earlier than first thought – proved to be incorrect.
In fact, the genetic sequence identified in October was for the prevalent Delta variant of the virus, Nigerian health authorities said.
Saudi Arabia became the first Gulf state to identify an Omicron case on Wednesday. Authorities in Riyadh said the variant had been identified in a traveller arriving from a north African country, without naming it.
In Asia, South Korea confirmed its first cases, and Japan asked international airlines to stop taking new reservations for all flights arriving in the country until the end of December in a further tightening of already strict border controls. The transportation ministry said the request was an emergency precaution.
The move by the world’s third-largest economy, coupled with its recent return to a ban on foreign visitors, is among the most stringent anywhere, and more in line with its cloistered neighbour China than with some other democracies in the region.
This week the World Health Organization urged countries to avoid blanket travel bans.
Japan has confirmed a second case of the Omicron variant in a person who arrived from Peru, one day after it reported its first case in a Namibian diplomat.
Scientists are working frantically to determine how threatening Omicron is. Much remains unknown about the new variant, which has been identified in more than 20 countries, including whether it is more contagious, whether it makes people more seriously ill, and whether it can thwart the vaccine.
Dr Anthony Fauci, the top US infectious disease expert, said more would be known about the variant in two to four weeks as scientists grow and test lab samples of the virus.