One of Professor Heneghan’s colleagues, Professor Trisha Greenhalgh, has conducted a systematic review of the evidence for masks. Unlike Professor Heneghan, I make my living analysing and interpreting observational data. I am extremely familiar with what one can and cannot usefully do with it in public health. I am moderately convinced by the evidence.
The evidence that masks protect a person from infection, particularly this type of mask or the cloth masks some members are wearing, is very low but the evidence that they reduce spread from an infected person is much better.