Masks Do More Than Protect Others During COVID-19: Reducing the Inoculum of SARS-CoV-2 to Protect the Wearer
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Department of Medicine, Division of HIV, Infectious Diseases and Global Medicine, University of California, San Francisco (UCSF) San Francisco, CA, USA; 2Desmond M. Tutu Professor of Public Health and Human Rights, Johns Hopkins Bloomberg School of Public Health Baltimore, MD, USA.
Although the benefit of population-level public facial masking to protect others during the COVID-19 pandemic has received a great deal of attention, we discuss for one of the first times the hypothesis that universal masking reduces the “inoculum” or dose of the virus for the maskwearer, leading to more mild and asymptomatic infection manifestations. Masks, depending on type, filter out the majority of viral particles, but not all. We first discuss the near-century-old literature around the viral inoculum and severity of disease (conceptualized as the LD50 or lethal dose of the virus). We include examples of rising rates of asymptomatic infection with population-level masking, including in closed settings (e.g., cruise ships) with and without universal masking. Asymptomatic infections may be harmful for spread but could actually be beneficial if they lead to higher rates of exposure. Exposing society to SARS-CoV-2 without the unacceptable consequences of severe illness with public masking could lead to greater community-level immunity and slower spread as we await a vaccine. This theory of viral inoculum and mild or asymptomatic disease with SARS-CoV-2 in light of population-level masking has received little attention so this is one of the first perspectives to discuss the evidence supporting this theory. J Gen Intern Med DOI: 10.1007/s11606-020-06067-8 © Society of General Internal Medicine 2020
outlines a unique angle on why universal T hispublicperspective masking during the COVID-19 pandemic should be one of the most important pillars of disease control. Our theory is based on the likelihood of masking reducing the viral inoculum to which the mask-wearer is exposed, leading to higher rates of mild or asymptomatic infection with COVID19. No prior perspective has specifically focused on this link between population-level facial masking, the viral inoculum, and increasing rates of asymptomatic infection with SARSCoV-2.
Received June 22, 2020 Accepted July 15, 2020
On April 3, 2020, the Centers for Disease Control and Prevention issued recommendations on wearing cloth face coverings by the public to reduce community spread.1 The World Health Organization did not recommend populationlevel face masking in April,2 but changed their guidance on June 5, 2020,3 when the extent of transmission from presymptomatic or even asymptomatic individuals was clear.4, 5 One recent model showed that population-level masking is one of the most efficacious interventions to reduce further spread of SARS-CoV-2, allowing for less-stringent lock-down requirements in countries adopting this strategy.6 Countries worldwide have had a range of responses to the recommendation on universal masking, with many countries (and US states)7 issuing mandates and enforc
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