Face masks needed for Covid-safe offices | Letter

The longer you spend in an aerosol-rich environment such as a poorly ventilated office with someone who is infected, the greater the risk, say Dr Helen Davison, Dr Finola O'Neill, and Dr Jonathan Fluxman

The health secretary is plain wrong when he says face masks do not work in offices because you're there for a long time" with other people (Senior doctors warn second coronavirus wave could devastate' NHS, 19 July). The risk of transmission of Covid-19 is directly related to viral load and exposure time, so the longer you spend in an aerosol-rich environment such as a poorly ventilated office with someone who is infected, the greater the risk.

If masks don't work because people share the same space for a long time, why is it mandatory for hundreds of thousands of healthcare workers to wear them all day at work? Yes, masks can be uncomfortable, they may become damp and need changing, but they are an indispensable tool alongside hand-washing and distancing in indoor environments, which is where most Covid-19 outbreaks occur.