Over the course of the pandemic, almost all of us have learnt something about respiratory illnesses, vaccines and public health.

 

But it is difficult to understate the extent to which, even at the highest echelons of science, our collective understanding of airborne transmission has changed during the last two years. This article, published in Wired last year, tells the story of how Covid transmission forced a re-evaluation of how viruses can spread. With Covid, rather than just falling fairly close the to the infected person in droplets, the virus also exists in the air – travelling long distances and hanging around for a while. This dawning realisation – at the WHO, the CDC, the UKHSA and others – led to changes in advice.  If it’s the air itself that is infectious, ventilation and space are key, not handwashing.

Catching On

The change rested on identifying a decades-old mistake that drew a line – at 5 microns – between airborne and droplet-based pathogens. Before now, pathogens smaller than 5 microns (e.g. tuberculosis) were considered airborne, anything bigger wasn’t. What we know now is that the line should be drawn at around 100 microns, not 5. That is a huge difference: rather than a handful of diseases being potentially airborne there are now hundreds, thousands. At the start of the pandemic we thought you could catch Covid from somebody sitting across from you. Now we know you can catch Covid from somebody across the other side of the restaurant. You can catch it from somebody who left the restaurant before you even walked in.

The revelation’s impact on Covid is likely to have been relatively muted – the 5-micron myth persisted throughout 2020 and only in April 2021 (18 months after the first cases were identified in Wuhan) did the WHO update its guidance, without fanfare.

The bigger impact may be on the behaviours and attitudes that prevail after Covid or as it becomes endemic – in response to future spikes in cases or even the regular, seasonal increase in respiratory illness that occurs most winters. If we understand, as we now do, that the air itself is infectious that we don’t need to be close to a coughing or sneezing person to catch what they’ve got – it could be another Covid variant, it could be the flu – are we not likely to adapt our behaviour, perhaps permanently?

In our view, permanent adaptations fall into three categories.

Firstly, public health. Ventilation in public buildings (from schools and hospitals to public sector offices) becomes an essential aspect of the nation’s public health. Ventilation and airflow are mandatory health considerations for businesses and property developers. NHS Trusts develop ‘green’ and ‘red’ hospitals to keep elective surgery and ongoing care separate from seasonal respiratory illnesses.

Second, personal adaptations. Mask wearing is not enforced but strongly seasonal as people look to avoid catching and spreading viruses when the weather gets colder. Other adaptations include avoiding public transport and reduced office working in winter.

Finally, consumer demands. Space and ventilation become consumer demands in leisure and hospitality contexts. The cosiness and atmosphere of a busy, lively restaurant is relegated behind ventilation, space and airflow in the consumer mindset. Footfall in these venues is reduced. More interactions move online or outdoors in the winter.

The threats of Covid will recede. Future Christmases are unlikely to be like this most recent one, with cities and offices deserted as people hunker down in fear of catching a virus that would force them to isolate rather than celebrate. But equally it would be naïve to expect behaviours to be unchanged by the pandemic – especially now that we know what we do about airborne risk.