The United States has a shortage of personal protective equipment. Every surgical mask and N95 respirator should be prioritized to frontline healthcare professionals. However, should the general public be wearing non-medical masks (i.e. cloth masks, scarves, bandanas, etc)?
This topic is controversial. As of April 2, the CDC in the United States recommended to only wear face masks if sick.
However, the CDC in China does recommend wearing face masks in public.
Academic clinicians in the New England Journal of Medicine state that wearing a mask outside a hospital offers little protection (Klompas et al. NEJM 2020).
However, many people on Twitter, including the former FDA chief Scott Gottlieb, suggest the countries that flattened the curve of disease all had public mask wearing policies.
Who is right? In this post, I’ll talk about the evidence for public mask wearing and the evidence for non-medical masks to quell respiratory infections.
Public Masks during 2003 SARS
Our current COVID-19 coronavirus is similar in biology, viral transmission, and danger to the 2003 SARS virus that stemmed from Hong Kong.
Lau et al. showed that during the 2003 SARS outbreak, wearing a mask in public was a protective preventive measure in reducing the risk of infection (Odds ratio of 0.27, p value < 0.001).
Similarly, Wu et al. also showed that wearing a mask in public, either sometimes (Odds Ratio 0.5, p = 0.02) or always (Odds Ratio 0.3, p < 0.001) was protective in preventing SARS.
It is pretty clear from both studies that wearing masks in public prevents SARS infection.
Medical vs Non-Medical Masks
We also know from the 2003 SARS virus that the greatest at-risk population were frontline healthcare workers. Every respirator and surgical mask should be prioritized to these individuals. But how effective are non-medical masks for the general population to prevent community transmission?
Dr. Sui Huang answered this question in a beautiful Medium post, stating that we should all wear masks in public even if they are homemade. Briefly, Huang argued that public mask wearing can help flatten the curve by at least 50%, which can help our overburdened healthcare system and save us time to build respirators, diagnostic tests, therapeutic drugs, and protective equipment to send to our hospitals.
Cloth based masks prevent 67% of particles from entering your mouth from the environment and prevent 10% of your cough from leaking into the environment.
Historical Evidence for Public Non-Medical Masks
There is also historical evidence that publicly mandated non-medical masks are effective.
For example, during the Spanish flu of 1918, a range of interventions were tried to quell the pandemic including banning of mass gatherings, mandated mask wearing, isolation, and disinfection (Bootsma and Ferguson, PNAS 2007). Cities that implemented these programs earlier and longer had fewer deaths (Strochlic and Champine).
Dr. Capps also showed mandated non-medical masks to be effective to prevent respiratory illness in an Army military camp (Capps, JAMA 1918). After the mask mandate, they reduced infection from scarlet fever and measles by greater than 95%. These results were replicated by Dr. McLester to control a bronchopneumonia outbreak at a hospital in Alabama and Dr. Lichty to control another pneumonia outbreak at Mercy Hospital in Pittsburgh.
In a personal protective equipment shortage, all medical masks (surgical and N95) should be prioritized to healthcare frontline workers. However, there is good evidence to suggest that public non-medical masks are beneficial.
As of April 3, the US CDC now recommends cloth masks for everyone when they go outside. This is a major development and a step in the right direction.