A subvariant of the Covid Delta strain could be more infectious than its ancestor, experts warned today after data revealed the proportion of cases linked to the strain has doubled in a month. AY.4.2, as it is currently known to scientists, made up almost 10 per cent of all infections in England in the fortnight ending October 9. Virus-trackers at the Wellcome Sanger Institute, which sequences thousands of Covid samples every week, say its prevalence stood at just four per cent in mid-September. Academics estimate it may be up to 15 per cent more transmissible than the original Delta, which...