Rapid response to: Face masks for the public during the covid-19 crisis – BMJ

In conclusion, as opposed to Greenhalgh et al., we believe that the context of the current covid-19 pandemic is very different from that of the “parachutes for jumping out of aeroplanes”,[7] in which the dynamics of harm and prevention are easy to define and even to quantify without the need of research studies. It is necessary to quantify the complex interactions that may well be operating between positive and negative effects of wearing surgical masks at population level. It is not time to act without evidence.