THE Covid-19 particle averages 0.125 microns in size, ranging from 0.06 to 0.14 microns.

It can only be seen by using an electron microscope.

Even the best face masks only filter down to 0.3 microns, so they present no guaranteed barrier to the virus passing in either direction.

Of course, some viral particles are intercepted and stick to the material, which presents a warm, damp environment and provides a perfect reservoir for the virus to duplicate.

Asymptomatic carriers (estimated to be 85 per cent of all people tested) are cheerfully going about their business and risking the lives of others by using masks that they don and remove using contaminated fingers. This is called fomite transmission.

Do not be surprised if after the new rules on mask wearing come into force, the rate of infection increases.

DW Lacey, Durham