Professor Carl Heneghan:

Within our World Health Organization advisory role we are specifically looking at transmission dynamics, including aerosol, fomite, oral-faecal and vector transmission. The Chairman is talking about laboratory-based evidence to show that if a person puts a mask on perfectly and wears it, then it reduces the aerosol spread in a laboratory situation. Is there any real-world evidence of that? No, there is not. People should look at the evidence in a critical way. If we consider the way people wear masks and the type of masks they wear - there is emerging evidence that some are better than others - there is no real-world evidence, but there is laboratory-based evidence.