Scientists now know that the coronavirus can transmit in the air through particles called aerosols that an infected person breathes out. These tiny particles, which can remain suspended in the air for hours, pose a high risk of infecting people in indoor spaces. But how risky is it, exactly, to spend time with people inside—a consideration many are weighing as the weather starts to turn?
A new visualization created by graphics journalist Mariano Zafra and published by the Spanish newspaper El País examines three common indoor situations, and shows how the virus can spread through the air if someone in the room has COVID-19. It’s based a model called the Estimator—created by University of Colorado Boulder chemistry professor Jose-Luis Jimenez—which approximates how coronavirus-containing aerosols move around indoor spaces. The visualization provides a stunning look at how infection risk drops when certain mitigating tactics are used.
For instance, the visualization illustrates a social gathering of six people, all of whom are keeping their distance in an unventilated room in someone’s home. If one person is infected and the group spends four hours together while speaking loudly, Jimenez’s model predicts that five will get the coronavirus. According to the model, mask-wearing doesn’t make a huge difference in this scenario—four out of five people will still be at risk of infection because they’ve been exposed for so long. But if everyone wears masks, the gathering is only two hours instead of four, and the room is ventilated—either mechanically or by opening the window and a door to ensure airflow—the risk for everyone drops dramatically. This information could inform how individuals, businesses, and schools avoid superspreader events and keep people safe during indoor gatherings.
The accompanying article, which was written by Javier Salas and translated into English by Heather Galloway, goes on to explore two other situations: an indoor bar and a classroom. In all cases, wearing masks mitigates some of the spread, and excellent ventilation makes a huge difference to how many people are infected.
The underlying model the visualization is based on, which was released in June 2020 and currently resides in a sharable Google Sheet, is derived from Jimenez’s primary focus and expertise: how pollution particles move through the air. It also provides data on aerosol spread in other situations, like while riding a bus, attending a protest, and going to the supermarket. However, the numbers in the visualization shouldn’t be taken as certainties. Though the model is based on peer-reviewed science, it’s still unclear exactly how much virus an infected person sheds, and how much ill-fitting cloth masks reduce the risk of catching the disease. The model also assumes that everyone maintains a two-meter distance from each other at all times.
“So we trust the order of magnitude of the results and especially the relative strengths of different actions such as increasing ventilation or wearing masks, but not the precise infection probabilities,” Jimenez said in a June press release. “Different actions have very different costs, so the hope is that the tool can help allocate limited resources to reduce the risk of infection most effectively.”
Check out the entire visualization here.