Omicron has been detected in 38 countries but there are no reported deaths so far from the new Covid-19 variant, the World Health Organisation said on Friday.
A WHO spokesperson told reporters that the UN health agency had "not seen reports of Omicron-related deaths yet".
And Maria Van Kerkhove, the WHO's technical lead on Covid-19, said Omicron had been reported in 38 countries, with the variant now spread across all six WHO regions.
The WHO has said it will take several weeks to determine how infectious Omicron is, and to assess how vaccines, tests and treatments hold up against it.
But it insisted on Friday that scientists were well on top of it and would be able to produce those answers soon.
"We're going to get the answers that everybody out there needs," WHO emergencies director Michael Ryan said.
"We need to trust in the science now and be patient and not be fearful."
Van Kerkhove told viewers on social media there were some suggestions that the variant was showing increased transmissibility — but it would take a few more days to get a clear picture.
As for severity, the initial reports came from a cluster of university students and younger people tend to present milder disease, she said.
Of the mild Omicron cases found so far, Van Kerkhove said they were mainly travellers — and people who were sick would not be getting on planes in the first place.
Therefore, it is "really too soon" to draw conclusions about Omicron's severity, she said.
On vaccines, the WHO stressed there was no reason to doubt the effectiveness of the current vaccines.
"Right now there is no need to change the vaccines we're currently using," said Ryan.
"There is no evidence to support that. But there's a lot of work going on to look at if we were to change, how might we change those vaccines?
"Get vaccinated. Right now that's your best bet."
Omicron was first reported to the WHO from South Africa on November 24, while the first known laboratory confirmed case was identified from a specimen collected on November 9.
Van Kerkhove said a backlog of virus sequences had built up in November, meaning some of the earliest cases may yet be found outside South Africa.
The Delta variant accounts for 99.8 per cent of sequences uploaded to the GISAID global science initiative with specimens collected in the last 60 days.
"Delta has outcompeted all of the other variants circulating. With Omicron, we have to see what happens," said Van Kerkhove.
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