- Airborne transmission may explain some perplexing superspreading events when distancing and hygiene rules were followed
How does coronavirus spread? Scientists are increasingly convinced that airborne transmission plays a role. Last week, more than 200 specialists penned an open letter to the World Health Organization urging it to officially accept that the Covid-19 virus can spread through the air further than social distancing recommendations.
The WHO says the possibility cannot be ruled out but its reluctance so far to embrace airborne transmission has put it at odds with aerosol chemists and engineers, who now believe the virus can spread through tiny particles that stay aloft for hours on air currents, in addition to the usual accepted route of larger droplets of saliva and mucus sprayed out from coughs and sneezes. The tension highlights the dilemma of using incomplete and potentially outdated scientific evidence to make critical judgment calls in a rapidly changing situation.
The virus is worryingly contagious, with nearly 13m confirmed cases worldwide. Droplets (defined as particles at least 5-10 microns across) are widely regarded as the master key to respiratory infection. They can be expelled in coughs and sneezes, as well as by singing, shouting and talking. Due to gravity, droplets generally fall to the floor within several metres — hence the need for distancing. Infection can occur directly, when virus-laden droplets enter the eyes, mouth, or nose of another person, or indirectly, when a person touches a surface on which droplets have fallen and then transfers the virus to their own eyes, mouth or nose, which explains handwashing guidance.