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This letter demonstrates that countries in which the public wears masks have a lower coronavirus-related mortality than in non-mask wearing countries.
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Country-wide coronavirus mortality and use of masks by the public.
Christopher T. Leffler, MD, MPH.1,2 Edsel Ing MD, MPH, CPH, MIAD.3
Joseph D. Lykins V, MD.4,5 Craig A. McKeown, MD.6
Andrzej Grzybowski, MD, PhD, MBA.7
1. Department of Ophthalmology. Virginia Commonwealth University. Richmond, VA 23298.
2. Department of Ophthalmology. Hunter Holmes McGuire VA Medical Center, Richmond, VA.
3. Department of Ophthalmology & Vision Sciences, University of Toronto.
4. Department of Internal Medicine, Virginia Commonwealth University. Richmond, VA 23298.
5. Department of Emergency Medicine. Virginia Commonwealth University. Richmond, VA 23298.
6. Bascom Palmer Eye Institute, University of Miami, Miller School of Medicine.
7. University of Warmia and Mazury, Olsztyn, Poland; Head of the Institute for Research in
Ophthalmology, Poznan, Poland.
April 22, 2020.
[This letter is cited: Leffler CT, Ing E, Lykins JD, McKeown CA, Grzybowski A. Country-wide coronavirus
mortality and use of masks by the public. Submitted for publication April 22, 2020. Available from:]
Face masks worn by the public might reduce the prevalence of the novel coronavirus
disease (COVID-19), in part by preventing the spread of respiratory droplets.1,2 We
hypothesized that countries in which the public typically used masks might have a lower
per-capita mortality from COVID-19 compared with non-mask wearing countries. Data
from 169 countries for which coronavirus mortality and testing data were available were
retrieved from a publicly available source on April 22, 2020.3 On average, the time from
infection to symptoms is 5.1 days, and that from infection to death is 23 days.1
Therefore, the date of each country’s initial infection was estimated as the earlier of: 5
days before the first reported infection, or 23 days before the first death.3,4 As deaths
by April 22, 2020 would typically reflect infections beginning 23 days previously (by
March 30), both the time from the first infection, and from the time the public began
wearing masks, until March 30 were determined. Countries in which mask usage has
been widespread include Hong Kong, South Korea, Malaysia, Taiwan, Japan, and
Mongolia.1,5 Mandates for wearing of masks in public had been issued by March 30 in
Thailand (March 12), Vietnam (March 16), Czechia (March 19), and Slovakia (March
25).1 The exponential growth associated with the spread of an epidemic appears linear
on a logarithmic scale.1 By multivariable linear regression, significant predictors of the
logarithm of each country’s per-capita coronavirus mortality included: duration of
infection in the country, duration of wearing masks, population size, and per-capita
testing (all p<0.001, Table 1). In a population not wearing masks, the per-capita
mortality tended to increase each week by a factor of 100.156 = 1.43, or 43%. On the
other hand, in a population wearing masks, the per-capita mortality tended to increase
by a factor of 10(0.156-0.144) = 1.028, or just 2.8%. The positive association with testing
probably reflects the greater recognition of coronavirus-related mortality with more
testing, as well as the increased incentive countries have to test when they suffer a
more intense outbreak. These results support the universal wearing of masks by the
public to suppress the spread of the coronavirus. Mask-wearing should be adopted
immediately, based on the precautionary principle.1,2
1. Leffler CT, Ing E, McKeown CA, Pratt D, Grzybowski A. Final Country-wide Mortality
from the Novel Coronavirus (COVID-19) Pandemic and Notes Regarding Mask Usage
by the Public. April 4, 2020. Available from:
19_Pandemic_and_Notes_Regarding_Mask_Usage_by_the_Public DOI:
2. Howard J, Huang A, Li Z, Tufekci Z, et al. Face masks against COVID-19: an
evidence review. Preprints 2020; published online April 12.
DOI:10.20944/preprints202004.0203.v1 (preprint).
3. Worldometers. COVID-19 Coronavirus Pandemic. Available from: Accessed
April 22, 2020.
4. European Centre for Disease Prevention and Control. COVID-19 Coronavirus data.
Available from:
Accessed April 16, 2020.
5. Feng S, Shen C, Xia N, Song W, Fan M, Cowling BJ. Rational use of face masks in
the COVID-19 pandemic. Lancet Respir Med. 2020 Mar 20. pii: S2213-2600(20)30134-
X. doi: 10.1016/S2213-2600(20) 30134-X.
None of the authors has any conflicts of interest to disclose.
Table 1. Predictors of (log) Country-wide Per-capita Coronavirus Mortality by
Multivariable Linear Regression in 169 Countries.
Coefficient (SE)
95% CI
Duration in
country (weeks)
0.156 (0.034)
0.089 to 0.223
Time wearing
masks (weeks)
-0.144 (0.033)
-0.209 to -0.079
Population (log)
-0.297 (0.079)
-0.453 to -0.141
Tests per capita
0.612 (0.085)
0.445 to 0.779
-2.571 (0.368)
-3.299 to -1.844
Full-text available
The science around the use of masks by the general public to impede COVID-19 transmission is advancing rapidly. Policymakers need guidance on how masks should be used by the general population to combat the COVID-19 pandemic. Here, we synthesize the relevant literature to inform multiple areas: 1) transmission characteristics of COVID-19, 2) filtering characteristics and efficacy of masks, 3) estimated population impacts of widespread community mask use, and 4) sociological considerations for policies concerning mask-wearing. A primary route of transmission of COVID-19 is likely via small respiratory droplets, and is known to be transmissible from presymptomatic and asymptomatic individuals. Reducing disease spread requires two things: first, limit contacts of infected individuals via physical distancing and contact tracing with appropriate quarantine, and second, reduce the transmission probability per contact by wearing masks in public, among other measures. The preponderance of evidence indicates that mask wearing reduces the transmissibility per contact by reducing transmission of infected droplets in both laboratory and clinical contexts. Public mask wearing is most effective at stopping spread of the virus when compliance is high. The decreased transmissibility could substantially reduce the death toll and economic impact while the cost of the intervention is low. Thus we recommend the adoption of public cloth mask wearing, as an effective form of source control, in conjunction with existing hygiene, distancing, and contact tracing strategies. We recommend that public officials and governments strongly encourage the use of widespread face masks in public, including the use of appropriate regulation.
Full-text available
Background. Many authorities have assumed that the novel coronavirus (COVID-19) pandemic will inevitably infect large fractions of the population in most countries. In addition, public health authorities and governments have varied in their policies regarding the use of face masks by the public. Methods. Mortality data from COVID-19 and policies regarding mask usage in various countries were compiled from publicly available sources. Results. The per-capita mortality approaches an upper bound which varies substantially between regions, from close to 1 in 3,200 dead in Italy and Spain, to less than 1 in 1,000,000 dead in other regions (e.g. Japan, Hong Kong, Taiwan, Slovakia). Numerous countries which have maintained their mortality asymptote orders of magnitude below that of the hardest-hit regions have widespread adoption of masks by the public. The mortality curve of the Czech Republic following a mandate for public mask usage on March 19, 2020 is consistent with a levelling off of mortality, with avoidance of the high upper bound of mortality seen in much of the West. Conclusions. There is up to 3 orders of magnitude of variation between regions in the total fraction of the population killed by the coronavirus well after the disease becomes established. Therefore, widespread infection with the coronavirus in a country is not inevitable—some countries have substantially controlled the spread of the disease. Public mask usage is one of several plausible explanations for the mortality reduction in some regions. The benefit of broad public use of masks might be better established by the end of April 2020, when the mortality trajectories in Western regions recently mandating mask usage are known. In the meantime, broad adoption of public mask usage is a reasonable strategy for infection control which should be adopted on the precautionary principle.
COVID-19 Coronavirus Pandemic
  • Worldometers
Worldometers. COVID-19 Coronavirus Pandemic. Available from: Accessed April 22, 2020.
Rational use of face masks in the COVID-19 pandemic
  • S Feng
  • C Shen
  • N Xia
  • W Song
  • M Fan
  • B J Cowling
Feng S, Shen C, Xia N, Song W, Fan M, Cowling BJ. Rational use of face masks in the COVID-19 pandemic. Lancet Respir Med. 2020 Mar 20. pii: S2213-2600(20)30134-X. doi: 10.1016/S2213-2600(20) 30134-X.