As time goes on we are learning more and more about the transmission of coronavirus, especially in airborne particles – basically by breathing in the virus from the air.
When we do that we’re inhaling “aerosols”. Distance is important here and inhalation of virus particles is most likely to happen when we’re close to someone who’s breathing them out.
This is because at close quarters aerosols concentrate and become dense. Think of standing close to someone who’s smoking.
As Julian Wang of Leicester University and colleagues point out in the BMJ, people infected with coronavirus breathe out many small particles laden with the virus.
Some of these will be inhaled almost immediately by people within a conversational distance (less than one metre). The rest will travel longer distances to be inhaled by others further away (more than two metres).
Why does distance matter? Well, if we abide by the rules, most of the time it doesn’t. By wearing masks, keeping our distance and avoiding crowded places we’ll avoid inhaling aerosols. But as the tiniest particles can remain airborne for hours, ventilation – open doors and windows – become crucial to drive particles out of reach.
Masks are quite efficient at impeding large droplets from landing on your face, but are only partially effective against inhaling aerosols because tiny particles can enter around any gaps between the mask and your face.
If the virus was only transmitted through larger particles (droplets) that fall to the ground within a metre or so after exhalation, then mask fit would be less of a concern.
As it is, even healthcare workers wearing surgical masks have still become infected.
With the airborne spread of coronavirus now fully recognised, we’re still only just understanding which activities generate aerosols.
But given that we can now accept that coronavirus transmits mostly between people at close range through inhalation, it’s a good idea to keep your everyday conversations brief and at more than a one-metre distance.
I think Covid-19 will probably become seasonal and we’ll have to learn to live with it as we do with flu.
Improving indoor ventilation and air quality, particularly in the areas of healthcare, work and education, will help all of us to stay safe, now and in the future.