The writer is a science commentator

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 The tension highlights the dilemma of using incomplete and potentially outdated scientific evidence to make critical judgment calls in a rapidly changing situation.