The heavily mutated Omicron variant is rapidly becoming the dominant strain of the coronavirus in South Africa less than four weeks after it was first detected there, Reuters reports.

South Africa's National Institute for Communicable Diseases said early epidemiological data suggested Omicron was able to evade some immunity, but existing vaccines should still protect against severe disease and death.

It said 74 per cent 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 November 8 in Gauteng, South Africa's most populous province.

The number of new cases reported in South Africa has doubled from Tuesday to Wednesday.

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