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:
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.
3. Worldometers. COVID-19 Coronavirus Pandemic. Available from:
April 22, 2020.
4. European Centre for Disease Prevention and Control. COVID-19 Coronavirus data.
Available from: https://data.europa.eu/euodp/en/data/dataset/covid-19-coronavirus-data
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.
0.089 to 0.223
-0.209 to -0.079
-0.453 to -0.141
Tests per capita
0.445 to 0.779
-3.299 to -1.844