Some data has crumbled like icing sugar at the merest whiff of a challenge. Sadiq Khan quoted some quite astonishing figures: that someone not wearing a face covering had a 70% risk of transmitting the virus, but by wearing a mask the risk was reduced to 5%, dropping to 1.5% if both parties were wearing masks.16 The source was the British Medical Association (BMA). I contacted the BMA, which claimed that their Medical Academic Staff Committee and Public Health Medicine Committee had produced the calculations. Seven emails, two tweets and one phone call later, it turned out these figures had
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