The World Health Organization (WHO) does not yet have enough data on the new Omicron variant of the coronavirus to say if it is more transmissible than the Delta variant, an official said on Wednesday, almost a month after South Africa first raised the alarm about its emergence.

"We have not seen this variant circulate for long enough in populations around the world, certainly in vulnerable populations," said the WHO's technical lead on COVID-19, Maria van Kerkhove, in a briefing with media.

She said the data on the new variant, first identified in southern Africa and Hong Kong in November, was still "messy" as countries reported its arrival and spread.