Mask wearing found to be better than sheltering, social distancing for limiting COVID

Businesses in Fresno are reopening as California enters Stage 2 of its Resilience Roadmap. However, new cases of COVID-19 in Fresno County continue to accelerate, and so the risks of infection by visiting public spaces are ironically much greater now than when California instituted its shelter-in-place order. Business closures, though, are not the only tool that government officials can employ.

Studies of face masks show that they confer some protection to the wearer, and their widespread use may stop an epidemic. To understand the role of face masks it is important to understand COVID-related risks.

The CDC has emphasized that a principle viral pathway is “through respiratory droplets produced when an infected person coughs, sneezes, or talks.” These droplets can then “land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.” It is still possible to become infected by touching infected surfaces (then touching your face), and so frequent hand-washing is important. But the CDC now recommends that face masks should be worn by everyone when in public.

These recommendations are supported by laboratory experiments. Stadnytskyi et al. (2020) found that that “loud speech can emit thousands of oral fluid droplets per second,” which may hang in the air for several 8-14 minutes. However, Tang et al. (2009) and Lai et al. (2012) show that face masks can block a large fraction of such droplets, and Leung et al. (2020), measuring the viral concentrations of exhaled droplets, found that “surgical face masks could be used by ill people to reduce onward transmission.”

The CDC recommends cloth masks, perhaps from a concern that surgical and N95 masks are in short supply. As a form of personal protection, surgical masks are still better (McIntyre et al. 2015) while cloth masks are “better than no protection” (Davies et al. 2013). But studies also show that public spaces are safer when mask use is universal.

How many people must wear masks in public? A computer simulation by Kai et al. (2020) found that an 80% masking rate was more effective than either a strict lockdown or social distancing to prevent viral spread; 50% masking rates are ineffective, and social distancing alone would still lead to widespread infection. Their result confirms earlier computer simulations such as that by Yan et al. (2019) who found that an 80% masking rate “essentially eliminated” a simulated influenza outbreak. These studies emphasize the use of N95 masks (so-called because they block 95% of small particles), but other studies (Loeb et al. 2009; Johnson et al. 2009) indicate that surgical masks might be equally effective. In a randomized study of emergency-room visits, MacIntyre et al. (2008) found that masks conferred a “protective efficacy in excess of 80% against clinical influenza-like illness,” with no significant drop-off in protectiveness for surgical masks.

Epidemiological studies also provide a compelling case to enforce widespread masking. Lau et al. (2004) found that mask-wearing “played an essential role” in limiting infection rates during the 2003 SARS-cov1 epidemic in Hong Kong. And in the journal Science, Prather et al. (2020) note that countries that have “implemented universal masking” have lower SARS-coV2 (the virus that causes COVID-19) infection rates.

Hong Kong is an especially interesting contrast to Fresno in the current pandemic. Hong Kong has an open border with China, and its 7.4 million inhabitants are densely packed; it has also avoided lockdowns, but as one resident put it, “not wearing a mask is like not wearing pants” (WSJ, April 8th). Photos also show Hong Kong citizens not only wearing surgical-type masks —but wearing them properly, covering both mouth and nose. Hong Kong has reported just four COVID-19-related deaths and less than 1,100 infections. Meanwhile, Fresno County, with just 13% of Hong Kong’s population, with no border with China, and a vastly lower population density, has recorded 35 deaths and 1,743 total cases.

Masking rates are an effective tool that has been strangely underutilized by city and county officials. And the costs of universal masking are paltry compared to the costs of closing the economy or continued loss of life. MacIntyre et al. concluded that, “In a pandemic, we would expect [mask-wearing] compliance to improve.” This hasn’t yet happened in Fresno, much less the U.S., but it might not be too late to save lives and the U.S. economy.

This story was originally published June 2, 2020 at 6:00 AM.