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A subvariant of the Covid Delta strain could be more infectious than its ancestor, as data reveals it was linked with nearly one in 10 cases earlier this month.
The AY.4.2 strain was spotted in June by the Wellcome Sanger Institute, which sequences thousands of Covid samples in England every week.
And its prevalence has doubled in a month from four per cent in September to 8.9 per cent in the two weeks to October 9.
Experts estimate that it could be up to 15 per cent more infectious than the original Delta strain, which is dominant worldwide.
Some 45 different sub-lineages of the variant — which was first spotted in India — have been recorded so far.
No10 is keeping a close eye on AY.4.2 but said there is 'no evidence' that it spreads more easily.
The graph shows the proportion of cases sequenced in England that are the new subvariant AY.4.2 (yellow) and Delta (blue)
Professor Francois Balloux, director of the University College London Genetics Institute, told the Financial Times the strain could be the most infectious seen since the pandemic began.
But he noted Britain is the only country where the strain has 'taken off' so its quick growth could be a 'chance demographic event'.
The World Health Organization will likely elevate AY.4.2 to a 'variant under investigation', which means it would be given a name under its Greek letter naming system, Professor Balloux added.