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This graph has been making the rounds today on the effect of masks at reducing #SARSCoV2 #HCoV19 #COVID19 #coronavirus transmission. There's a lot more going on here than mask/no mask
First, there was so much mask-wearing in China that in early February there were mask shortages. China manufactures 20 billion masks a year, so those shortages affect places in the "masks" group too. https://www.scmp.com/economy/china-economy/article/3049170/why-china-grips-facial-mask-shortage-coronavirus-death-toll
Also China made mask-wearing mandatory in numerous provinces and cities in early February. China is not in the "no mask" category. https://www.scmp.com/news/china/society/article/3049891/beijing-and-shanghai-impose-new-controls-residents-china-battles
Other factors limited spread in the "masks" category. Singapore & Hong Kong implemented strict quarantine & distancing measures. In Japan, cultural etiquette reduces physical contact (ie handshakes). South Korea tested widely & isolated mild cases to break transmission chains.
These measures likely had a much more profound impact than "just wear masks." There's also debate about surgical masks. They can reduce respiratory droplet spread by infected people, but it's less clear that they are protective for uninfected people. https://www.sciencemag.org/news/2020/03/would-everyone-wearing-face-masks-help-us-slow-pandemic
Also if people are not wearing masks correctly it can increase risk of infection. I've seen way too many people pulling masks aside to eat or drink, touching them on the outside, reversing them, reusing them...these are all incorrect.
When people train to wear PPE, we also learn how to safely doff. If you touch the front of the mask and then touch your face, that's potential for exposure. If you are sick and touch the inside of the mask and then touch a surface, that's potential for contamination.
Also, there is no evidence that aerosol transmission occurs outside of aerosol-generating procedures in a hospital setting. Physical distancing is adequate protection for respiratory droplets.
I'd have no problem with mask wearing for reduction of respiratory droplet production IF frontline health care workers weren't subject to critical shortages of PPE. Under no circumstances should we deprive these heroes of the protection they need when we need it most.
In particular, non-HCWs should not wear or hoard N95 respirators. Not only do N95s need to be properly fitted to work correctly, these are absolutely critical for HCWs treating the most severely ill patients who need ventilation and other aerosol-generating procedures.
