LONDON, UK—The Delta coronavirus variant of concern, first identified in India, is believed to be 60 percent more transmissible than the Alpha variant which was previously dominant in Britain, a prominent UK epidemiologist said on Wednesday. British Prime Minister Boris Johnson has said that England’s full reopening from COVID-19 lockdown, pencilled in for June 21, could be pushed back due to the rapid spread of the Delta variant. Neil Ferguson of Imperial College London told reporters that estimates of Delta’s transmission edge over Alpha had narrowed, and “we think 60 percent is probably the best estimate.” Ferguson said that modelling suggested any third wave of infections could rival Britain’s second wave in the winter—which was fuelled by the Alpha variant first identified in Kent, south east England. But it was unclear how any spike in hospitalisations would translate into a rise in deaths, as more detail was needed on how …