Professor Raina MacIntyre: There is no randomised controlled trial of masks or distancing for COVID-19. In the absence of this, the best evidence we have is from trials of other respiratory viruses, or from observational studies of beta-coronaviruses.  This study synthesises all the available evidence specific to SARS, MERS and COVID-19 using the GRADE criteria, and gives us the best available evidence to date which is specific for coronaviruses. READ MORE