This Is How Many People Need to Wear Masks to Stop the Coronavirus

Not nearly enough Americans are wearing masks, according to new research out of UC Berkeley.

Throughout the coronavirus pandemic, you may have wondered, "Why do I need to wear a face mask?" "How effective are they really?" or "How many people need to wear face masks to stop coronavirus from spreading?" And as the U.S. teeters on the cusp of reopening, these questions are becoming more and more pressing. Now, new extensive research on face masks conducted by computer scientist De Kai, PhD, has the answers.

Kai—who has joint appointments at UC Berkeley's International Computer Science Institute and at the Hong Kong University of Science and Technology—built a sophisticated computer forecasting model called the masksim simulator. The model shows how different face mask policies work, accounting for randomness, small accidents, face mask efficacy, and other variables. (You can see the simulator in action via a video demonstration, and even access masksim online to use the model for research yourself.)

According to Kai's research, if 80 percent of a closed population wore masks, COVID-19 infection rates would drop to approximately one twelfth the number of infections, compared with a population in which no one wore masks.

The concerning part? Even when nearly half of a closed population wears masks, the benefits become next to nonexistent. "If you get down to 30 or 40 percent," Kai told Vanity Fair, "you get almost no [beneficial] effect at all."

So where does the U.S. stand in terms of Kai's goal rate? Unfortunately, well below that 80-percent threshold. As a country, about 49 percent of the population wears face masks, according to April data from YouGov. That makes us 15th out of the 26 global markets analyzed—behind places like Hong Kong (90 percent), China (89 percent), Italy (85 percent), India (84 percent), Japan (76 percent), and Saudi Arabia (59 percent), among others.

Based on Kai's research, we know that 49 percent of the U.S. population donning face masks just isn't going to cut it when it comes to eliminating the coronavirus. However, there are signs of hope that indicate we can get to that 80-90 percent sweet spot. After the Centers for Disease Control and Prevention (CDC) officially recommended the use of face masks in public places on Apr. 3, a Gallup poll conducted from Apr. 7 to Apr. 14 found that 62 percent of Americans reported wearing a mask outside of their home, up from 38 percent the week prior. We just need to continue on a similar trajectory to ensure we stay safe now that lockdowns are starting to lift.

As Kai's collaborator Guy-Philippe Goldstein, an economist and cybersecurity expert, told Vanity Fair: "What's most important about wearing masks right now is that it works, along with social distancing, to flatten the curve of infections as we wait for treatments and vaccines to be developed—while also allowing people to go out and some businesses to reopen." And for proper handling of your face mask, check out 7 Face Mask Care Mistakes You're Making.

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