A subvariant of the Covid-19 Delta variant that is growing in Britain is less likely to lead to symptomatic Covid-19 infection, a coronavirus prevalence survey found, adding that overall cases had dropped from a peak in October.

The Imperial College London REACT-1 study has found that the subvariant, known as AY.4.2, had grown to be nearly 12 per cent of samples sequenced, but only a third had "classic" Covid symptoms, compared with nearly a half of those with the currently dominant Delta lineage AY.4.

The researchers said that asymptomatic people might self-isolate less, but also that people with fewer symptoms might spread it less easily through coughing and also may be unlikely to get severely ill.

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