The new Omicron variant of COVID-19 is a “cause for concern and not for panic”, Joe Biden has said.
The US president told reporters his decision to restrict travel from countries in southern Africa “gives us time” to take more action.
The new variant was initially reported to the World Health Organisation (WHO) by South African scientists last Wednesday.
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“Sooner or later we’re going to see cases of this new variant in the United States,” Mr Biden said.
“It’s a cause for concern, not a cause for panic… We’re going to fight and beat this new variant as well.”
Mr Biden urged people to get fully vaccinated – and those who can to get booster jabs.
He added: “We do not yet believe that additional measures will be needed.”
Mr Biden said it would be weeks before the world knew how effective current vaccines would be against it.
Earlier, the WHO advised its 194 member nations that any surge in infections could have severe consequences, but said no deaths had yet been linked to the new variant.
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“Omicron has an unprecedented number of spike mutations, some of which are concerning for their potential impact on the trajectory of the pandemic,” a statement said.
“The overall global risk related to the new variant of concern Omicron is assessed as very high.”
Further research was needed to understand Omicron’s potential to escape protection against immunity induced by vaccines and previous infections, it said.