Scientists who track coronavirus mutations are closely monitoring an uptick in cases of an Omicron sub-variant named BA.2, just as countries were beginning to hope the worst of the latest wave of Covid-19 infections had passed.
The strain has been detected in 57 countries, according to the World Health Organization, and now accounts for about a tenth of Sars-Cov-2 genome sequences uploaded to the global repository Gisaid.
The original version of Omicron, designated as BA.1, is still responsible for most cases. Nevertheless, BA.2 has become the dominant variant in Denmark, India and South Africa.
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