As evidence accumulates about the transmission routes of the Covid-19 plague, can we afford any longer to allow unconstrained speaking in confined spaces?

My elder daughter has sent me an interesting and informed article from the English language edition of the Spanish El Pais newspaper, which is worth reading in full. Put simply, it shows how tiny aerosols – rather than, as first thought, the larger droplets – are particular spreaders of the plague in rooms with poor ventilation and and where people allow aerosols to escape from their mouths by speaking. Aerosols linger in the air much longer than droplets, and so are potentially more harmful.

This has an immediate practical implication. The anti-plague rules currently allow people with certain conditions to be exempt from the requirement to wear face coverings on buses and trains. I’m not a frequent bus user but judging by the number of people I see not wearing masks on our buses in Exeter we have a seriously disabled population.

Not wearing a mask is not in itself an issue: there are good reasons for the exemption when applied honestly. Concern arises when non-wearers decide to hold conversations on the bus. Because summer has passed and the weather is now colder and windier there is a greater temptation not to open the windows and ventilate the bus. So, in exchange for the concession of not having to wear a mask, some of those beneficiaries put the rest of us at greater risk by spewing their potentially plague-carrying aerosols around in an enclosed space.

Bus and train operators need to take this in hand. Two measures spring to mind.

First, ensure that at least two windows on every vehicle deck are fixed in the open postion so that no one can close them. If passengers complain, then they need to be reminded that it’s better to be chilled on public transport than frozen in a public mortuary.

Second, every passenger allowed to board without a face covering should be a handed a short leaflet by the driver or conductor. This would have on one side a clear large font instruction on the lines of “No mask? Then please don’t talk!” with an explanation on the other.

Not everyone will obey, but it would strengthen the hand of the rule-observant majority and – hopefully – get the infection rate down. As the old World War 2 slogan went: “Careless Talk Costs Lives”.