Experts have been recommending face masks as a way to prevent the spread of coronavirus; the wearer of the face mask can protect people around them because the mask blocks respiratory droplets, which have been identified as a main means of COVID-19 transmission. But could wearing a face mask also protect the wearer? It's a possibility, according to a new paper from researchers at the University of California – San Francisco and John Hopkins, which will be published in the Journal of General Internal Medicine.
The paper draws on "virologic, epidemiologic, and ecologic evidence" to make the argument that wearing a face mask could result in a lower "viral dose," or amount of coronavirus particles, taken in by a wearer exposed to the virus. And according to several studies cited by the researchers, a lower viral dose can lead to less severe symptoms, or even no symptoms at all, of a given illness, including COVID-19.
One cited study, published in May, tested this with coronavirus and hamsters. Researchers in China set up cages of hamsters, some infected with coronavirus and others healthy, and separated the two groups with partitions of surgical masks in some of the cages. In citing this study, the UCSF and Johns Hopkins scientists noted that the healthy hamsters were "less likely to contract SARS-CoV-2 infection with a surgical mask partition," and those that did had a milder infection compared to their "non-masked" peers.
The researchers also looked at large-scale coronavirus data from before and after face masking was widely practiced. A pre-masking review, they noted, estimated that 15 percent of COVID-19 cases were asymptomatic. A more recent review has placed that number as high as 40-45 percent, and the CDC has agreed that asymptomatic infection is around 40 percent. In the closed setting of a cruise ship, this narrative has also played out. An estimate in March put rates of asymptomatic infection on the Diamond Princess cruise ship at around 18 percent. On a more recent cruise, all passengers and staff were given masks after a positive case was identified onboard. While 128 out of 217 passengers eventually tested positive, 81 percent of them remained asymptomatic.
While this evidence is indirect, the researchers drew on it to hypothesize that face masks could play a role in increasing the proportion of cases that are asymptomatic, which, though problematic for transmitting the virus, could help communities reach herd immunity without large amounts of severe cases.
And it could even go beyond that, they suggest. Again noting that the evidence was indirect and likely impacted by multiple factors, the researchers nonetheless noted that countries with population-level masking have had more success in reducing death rates from COVID-19. "Indeed, even when cases have resurged in these areas with population-based masking upon re-opening (e.g. South Korea, Singapore, Hong Kong, Taiwan), the case-fatality rate has remained low with opening but masking," the researchers wrote. ThRead More – Source
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