We know that the virus spreads when people are in close contact, and according to the CDC, respiratory droplets that are produced when a sick person coughs or sneezes are the most common mechanism for transmission. These droplets don’t travel more than six feet from the sick person, which is why social-distancing rules use the six-feet marker.
However, there is also evidence that the virus can spread through small droplets produced during normal activity, like talking or laughing, and while larger droplets fall to the ground, according to a new study published in the Proceedings of the National Academy of Sciences and covered by the New York Times, these small droplets can remain suspended in the air for up to 14 minutes. Additionally, research shows that the virus is aerosolized, meaning it’s contained in even smaller droplets called aerosols that can travel through air. And in April, Chinese researchers released the results of a study that showed how air currents from a Guangzhou restaurant’s ventilation system carried aerosols to restaurant patrons more than six feet away from an infected diner. The study seemed to suggest that diners should be wary of ventilation systems — and that there might be “safe” places to sit in restaurants. But it’s not so simple.
Ultimately, though, ventilation works to mitigate the spread of the virus. Ventilation systems, if constructed properly — meaning that they’re delivering fresh outdoor air and recirculating air through a high-efficiency filter — help clean the air. “We’ve known about these factors for a long time in terms of how they can exacerbate a problem in a building or work to help mitigate disease,” says Allen. “It’s not so much that an air conditioner or any other system is inherently good or bad, it’s how it’s being operated and how the air is being delivered.”
While it’s possible for the virus to be carried in small droplets through the air, airflow can also disrupt aerosol transmission. According to Kevin Van Den Wymelenberg, director of Energy Studies in Buildings Laboratory at the University of Oregon, increasing airflow in a room, whether it’s through a ventilation system or opening windows to create a cross breeze, is one of three built-environment considerations that may reduce transmission. There’s also evidence to suggest that humidity supports immune function, prevents viral particles from being deposed deep into the respiratory tract, and has been shown to deactivate viruses. And while more data is needed, some preliminary research shows that sunlight can deactivate the virus in the same way it does for bacteria.