A study led by UCLA Fielding School of Public Health Professor Yifang Zhu has determined that even a simple cloth mask provides significant protections against COVID-19 transmission, reducing the spread of respiratory droplets by as much as 77%.
We found that a simple cough could send particles more than six feet away, without face coverings."
Yifang Zhu, Professor, Department of Environmental Health Sciences and Associate Dean for Academic Programs, UCLA Fielding School of Public Health
"At about a foot away from the coughing source, a face shield by itself provided the least protection (i.e., 4%). In contrast, a cloth mask reduced cough particles by 77%, and the combination of face shield and cloth mask improved the particle reduction to 89%."
The article, "Assessing the effectiveness of using various face coverings to mitigate the transport of airborne particles produced by coughing indoors" is published in the current electronic edition of the peer-reviewed journal Aerosol Science and Technology.
Zhu's team, which includes UCLA FSPH scholars Liqiao Li and Muchuan Niu, set up a test space in a lab and measured the particle number concentration (PNC) and particle size distribution under seven different conditions: (1) no face covering; (2) face shield only; (3) cloth mask; (4) face shield + cloth mask; (5) surgical mask; (6) face shield + surgical mask; (7) N95 respirator or equivalent (i.e., KN95 mask).
The research suggests that relatively simple measures like masking, combined with physical distancing, hand hygiene, and specific steps taken with regards to being indoors or outside, can make a significant difference in slowing the spread of COVID-19, which has resulted in more than 1.26 million deaths worldwide.
"To minimize the infection risk of aerosol transmission, stricter mitigation measures should be adopted for indoor environments, which are more likely to be enclosed and crowded," Li said. "One of the simplest is a mask."
Li, L., et al. (2020) Assessing the effectiveness of using various face coverings to mitigate the transport of airborne particles produced by coughing indoors. Aerosol Science and Technology. doi.org/10.1080/02786826.2020.1846679.