The Omicron variant is rapidly becoming the dominant strain of Covid-19 in South Africa less than four weeks after it was first detected there.
Cases have risen from a weekly average of 300 a day a fortnight ago to 3,500 a day. The number of new cases reported in South Africa doubled from Tuesday to yesterday.
South Africa's National Institute for Communicable Diseases (NICD) said early epidemiological data suggested that Omicron was able to evade some immunity, but existing vaccines should still protect against severe disease and death.
It said 74% of all the virus genomes it had sequenced last month had been of the new variant, which was first found in a sample taken on 8 November in Gauteng, South Africa's most populous province.