GIVEN that the PM and others have advised the continuing use of face coverings I thought that I would do a brief survey of which three-layer medical masks continue to be available to buy and which is best.

After visiting four high street pharmacies to check the packaging, I found that every manufacturer boasted of a 98 per cent bacterial filtration rate. None mentioned viral filtration - the very information a customer needs to know to make a good choice. Why? Because they don’t have to!

Isn’t it time, after 16 months, for manufacturers to be made to supply this crucial information? It cannot be as difficult or expensive to do as making a vaccine.

One store pharmacist told me that the Covid virus particle is over 50 times smaller than the average bacterium cell, so one of the masks would be as effective as a goal net stopping a marble.

A cynic might think that manufacturers have something to hide.

D Duell, Durham.

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