An interesting article published in MedRxiv showed that SARS-CoV-2 loses 90% of its ability to infect within five minutes of becoming airborne.  

The authors simulated how the virus survived in exhaled air.  

The findings re-emphasised the importance of short range COVID transmission with physical distancing and mask wearing likely to be the most effective means of preventing infection. 

Ventilation, though still worthwhile, was felt to have a lesser impact.  

The study suggested that as the viral particles left the relatively moist and carbon dioxide rich conditions of the lungs, they rapidly lost water and dried out.  

This led to a transition to lower levels of carbon dioxide associated with a rapid increase in pH.  These factors disrupted the virus’ ability to infect human cells, but the speed at which the particles dry out varies according to the relative humidity of the surrounding air. 

When this was lower than 50%, similar to the relatively dry air found in many offices, the virus had lost half of its infectivity within 10 seconds.  After this, the decline was slower and steadier. 

At 90% humidity, roughly equivalent to a steam or shower room, the decline in infectivity was gradual with 52% of particles remaining infectious after five minutes, dropping to about 10% after 20 minutes.  

However, the temperature of the air made no difference to viral infectivity contradicting the widely held belief that viral transmission is lower during warm weather.

Dr Paul Ettlinger

Translate »
Share This