Final Country-wide Mortality from the Novel Coronavirus (COVID-19)
Pandemic and Notes Regarding Mask Usage by the Public.
Christopher T. Leffler, MD, MPH.1,2 Edsel Ing MD, MPH, CPH, MIAD.3
Craig A. McKeown, MD.4 Dennis Pratt, MD.1,2 Andrzej Grzybowski, MD.5
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, University of Toronto.
4. Bascom Palmer Eye Institute, University of Miami, Miller School of Medicine.
5. University of Warmia and Mazury, Olsztyn, Poland; Head of the Institute for Research in
Ophthalmology, Poznan, Poland.
This paper may be cited: 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: researchgate.net. April 4, 2020.
Abstract. 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
The novel coronavirus (COVID-19) pandemic which began in 2019 has resulted
in substantial morbidity and mortality, has caused economic chaos, and has disrupted
the livelihoods and the daily lives of many millions worldwide. Like all infectious
diseases, COVID-19 has the capacity to expand in an exponential fashion, meaning that
it can rapidly spread to affect a very high percentage of the population. The mortality
observed to date could be a small fraction of what will be observed within a few
doubling times of the disease. On the other hand, with adequate suppression of
transmission, the exponential spread could be converted to an exponential decay,
resulting in a very low prevalence of the disease.
Face masks may decrease the spread of COVID-19. However, contradictory
recommendations have been issued regarding broad adoption of face masks by the
public. Some East Asian countries have used face masks to control this novel
In contrast, the World Health Organization recommended that
asymptomatic people should only wear a mask if caring for someone with suspected
Likewise, the United States Centers for Disease Control did
not initially recommend that people who feel well should wear a mask
, until very
recently (see below).
The purpose of this report is to discuss: 1) the fraction of the population which a
country might anticipate will ultimately die from COVID-19, and 2) the possible effect of
widespread adoption of face-covering with a mask (or bandana, scarf, etc.) on the
course of the pandemic.
We compiled the country-wide mortality related to the novel coronavirus (COVID-
19) from a sample of countries thought to be important prototypes of various public
health policies, or whose experience with the pandemic has been notable. Italy
were studied, because they have been hit especially hard by the virus.
We looked at several countries which varied in their testing response. The
United States had difficulty with fielding diagnostic tests, while Germany was one of the
leaders in testing. Also of note, the German government guidelines discouraged mask-
wearing by the public by quoting the WHO: “wearing a mask in situations where it is not
recommended to do so can create a false sense of security.”
Worldometers, Italy, 2020.
Worldometers, Spain, 2020.
Several Asian countries have recommended masks to be worn by the public
during this outbreak. Hong Kong recommended surgical or disposable masks for
people in crowded places.
Mainland China also recommended masks for most of the
The Japanese government declared that “If you wear a face mask in confined,
badly ventilated spaces, it might help avoid catching droplets emitted from others…”
Thailand, it was reported on March 12, 2020 that health authorities encouraged the
public to use home-made cloth masks. Panpimon Wipulakorn, Director-General for the
Department of Health in Thailand stated: “The droplet from coughing and sneezing is
around five microns and we have tested already that cloth masks can protect against
droplets bigger than one micron.”
Sweden was studied because they have not shut down or limited dine-in
restaurants and schools to the same extent as many other western countries.
Mandates of several Western nations for their public to use masks recently went
into effect: the Czech Republic on March 19, 2020,
Slovakia on March 24, 2020,
Austria on March 31, 2020 (in grocery stores), and Israel on April 1, 2020.
Therefore, we obtained mortality data from the novel coronavirus from the
Hopkins Coronavirus Resource Center,
confirming the numbers from other sources
when possible, for Austria,
the Czech Republic,
Israel, Hong Kong,
Spain, Sweden, Taiwan,
Thailand, and Vietnam. Country population statistics were also obtained from public
Fraction of the Population Expected to Die.
For countries in which the infection has been established for some period of time,
the mortality grows at first in an exponential fashion (which appears linear on a
logarithmic scale), with eventual approach towards an asymptote (upper bound) (Figure
Johns Hopkins, 2020.
Worldmeters, Austria, 2020.
Worldometers, China, 2020.
Ministerstvo Zdravotnictvi Ceske Republiky, 2020.
Worldmeters, Germany, 2020.
Worldometers, Hong Kong 2020.
World Health Organization, Situation Reports.
Ministry of Health, Singapore, Apr 3, 2020; 2020 coronavirus pandemic in Singapore, Wikipedia.
2020 coronavirus pandemic in Slovakia, Wikipedia.org; Schiffmann 2020.
1). The worst-hit countries, Italy and Spain, seem to be approaching a mortality
asymptote of 10-3.5, or about 1 in 3,200 of the population dying. Other countries which
adopt public health policies similar to those in Italy and Spain might presumably have a
total mortality which stays below this upper bound as well.
There are enormous differences in this mortality asymptote between countries.
Both mainland China and South Korea had vigorous outbreaks early on. In fact, the
mortality curve in South Korea was running in parallel with that of Italy early in the
outbreak (Figure 1). However, both China and South Korea have ultimately kept their
mortality below the 1 in 100,000 mark (according to the data reported by their
governments, Figure 1). Moreover, a number of Asian countries (Japan, Singapore,
Hong Kong, Taiwan, Thailand, and Vietnam) have kept their mortality below 1 in
1,000,000 dead (Figure 1). In fact, Vietnam’s mortality data was not illustrated because
that country reports no deaths from coronavirus, as of April 4, 2020.
Figure 1. Per-capita mortality from coronavirus, demonstrating that mortality tends to approach an
asymptote, which varies between countries.
Among the countries which have succeeded in keeping the coronavirus mortality
below 1 in 1,000,000 over a prolonged period, many wear masks (Hong Kong, Japan,
Thailand, Taiwan, Vietnam, and Slovakia) (Figure 2). Singapore has also maintained a
low mortality rate, though it has crept up just a bit recently, and the government
mandated mask use by the public on April 3, 2020 (Figure 2).
In an ever-increasing number of western countries, broad mask usage by the
public has recently been mandated or recommended: the Czech Republic (Mar. 19),
Slovakia (March 24), Austria (in grocery stores, March 31), Israel (April 1), and the
United States (April 3) (Figure 2). As the earliest among this group, all eyes will be on
the mortality experience of the Czech Republic. As it takes on average 23 days from
infection with coronavirus until death (see below), we may not see the full effect of the
mask mandate in the Czech Republic until April 11, 2020. Nonetheless, as of April 4,
2020, we can see that the coronavirus mortality curve in the Czech Republic looks a bit
less steep than in other western countries at this stage of their outbreak (Figure 2).
Figure 2. Per-capita mortality from coronavirus, with illustration of recommendations to use masks by the
We have demonstrated two key findings. The first is that the fraction of a
country’s population dying during the epidemic varies by several orders of magnitude,
between about 1 in 3,200 and 1 in 1,000,000. In other words, numerous countries have
succeeded not merely in delaying infections, but in actually preventing most of their
population from becoming infected.
Many have assumed that very high rates of infection were inevitable in the
population. Numerous scientists and politicians have floated the idea that infection
would keep going until 40% to 70% of the population was infected.
In their view, the only thing that would stop the infection was when so many
people had been infected that the virus was less successful at finding a susceptible host
(herd immunity). Under this scenario, the observed mortality could have been quite
high. For instance, if 50% of the population is infected and the mortality among those
infected is 2%, then 1 person out of every 100 in the population could die from infection.
According to this view, the purpose of the public health response was merely to
slow down the spread of the disease over a longer period of time (the so-called
"flattening the curve"), to avoid having the health system overwhelmed by the volume.
That view could have been true, but the data suggest otherwise. Even the
hardest-hit countries seem to approach a maximum level of mortality which is lower
than under the “herd immunity” scenario. For instance, Italy and Spain appear to be
approaching an upper bound of about 1 in 3,200 of the population dying.
Interestingly, the asymptote defining the total mortality varies substantially
between countries. Many regions approach a much lower mortality asymptote. South
Korea, for instance, had a mortality curve which closely paralleled that of Italy early in
the course. However, ultimately, South Korea controlled the situation, and approached
an asymptote of about 1 in 250,000 dead. In fact, some countries which took
aggressive measures at the outset seem to be approaching an asymptote of less than 1
in 1,000,000 dead (e.g. Hong Kong, Japan, Thailand, Taiwan, and Singapore).
Slovakia also has a mortality rate well below 1 in 1,000,000, but more time must elapse
to know if this record can be maintained.
Of course, the statement that the total mortality for a country approaches an
upper bound relates to the duration studied (months, rather than years) and other
relevant conditions. For instance, if countries open schools or businesses, relax social
distancing, stopped testing for the disease or wearing masks, etc., a new upper bound
for infections could be approached. Moreover, the virus will still circulate, and could
become endemic, producing occasional outbreaks at a lower level.
Because no antibody test has been widely deployed yet, we do not actually know
the fraction of the population infected. But we can estimate some upper and lower
bounds. For instance, we might presume that the countries with an asymptote of 1 in
1,000,000 dead have a fraction of the population infected which is about 300 times less
than those with an asymptote of 1 in 3,200. Therefore, in the highly unlikely scenario
that the spread of the infection in the high-mortality countries is limited only because
absolutely everyone is infected (100%), then the infection rate would be about 0.3% in
the low-mortality countries. As a lower bound, if we choose the other extreme, and
assumed that the virus had a very high mortality rate (say 5%), then the infection rate in
the low-mortality countries would be 1 in 50,000. Either way, it is clear that the
countries with very low mortality appear to be preventing infection in well over 99% of
their citizens (assuming their mortality reports are accurate).
The U.S. administration has stated that the virus, with social distancing measures
in place, could cause between 100,000 and 240,000 deaths in the coming months. The
administration has been criticized on the grounds that the workings of the model have
not been published, and therefore there is no way for outside scientists to evaluate their
assumptions. Our graphical analysis provides some support for the lower end of this
figure. Put simply, if the United States follows the pattern of Italy and Spain in
approaching an asymptote of 1 in 3,200 dead, this would be close to 100,000 dead in
the United States. Thus, our analysis provides some support for the lower end of this
figure. However, the trajectory followed will depend on the policies adopted. If we relax
social distancing or open businesses and schools, the number could be higher. On the
other hand, the CDC policy to recommend voluntary usage of masks by the public
announced on April 3, 2020 might lower the death toll (see below), especially if it is
The wide variation in observed mortality between countries might be explained
by myriad factors, including the widespread use of masks, amount of testing for COVID-
19, social distancing and “lockdown” policies, and customary methods of greeting (e.g.
shaking hands). It is incumbent on the high-mortality countries to study and understand
all of the factors at play in the more successful countries.
Could the differences relate to testing? Of course, a capable testing program for
both active and prior infection is key to understanding and controlling an epidemic. With
respect to coronavirus, Germany was a leader in testing, while the U.S. testing
capabilities lagged considerably. Germany does have a mortality curve a bit lower than
the U.S., but not by an order of magnitude. Thus, in this case, Germany’s early testing
capability has not resulted in a dramatically different per-capita mortality trajectory from
that in the United States.
Could the differences between high and low-mortality countries be accounted for
by closing businesses and schools? It certainly is a logical practice, because infections
are less likely to spread when people are separated. Sweden stayed largely open for
business, compared with the U.S. Indeed, Sweden has a per-capita mortality curve
slightly higher than that of the U.S. But again, the differences are not on the level of an
order of magnitude. Both countries seem to be on track to follow the path of Italy and
Spain towards the 1 in 3,200 mortality asymptote. Of course, it must be emphasized
that countries should be able to change their mortality trajectory through vigorous public
Could the differences between high and low-mortality countries be related to
wearing of masks by the public? Here, the differences appear to be striking. Almost
every country proven to have kept the asymptotic mortality to less than 1 in 1,000,000
for the entire outbreak has adopted widespread mask usage by the public.
The effect of mask usage by the public on mortality from coronavirus will likely be
substantially more clear by the end of April 2020, because we will be able to see the
ultimate mortality path followed by the Czech Republic, Slovakia, Israel, Austria, and the
United States all of which have mandated or recommended public mask usage too
recently to fully determine what the impact will be. The median incubation period
between coronavirus infection and the onset of symptoms is 5.1 days.
there are 17.8 days between developing symptoms of coronavirus infection and death.
Thus, it could easily be expected to take 23 days between implementation of a new
public health policy and full realization of the effect.
Singapore’s public was not initially advised by the government to wear masks.
However, the public in Singapore public likely had attitudes towards masks intermediate
between those in the West and some nearby regions. In 2004 (just after the 2003
SARS outbreak), 28% of the Singapore population had worn a face mask in public in
the previous two years, compared with 5% in the United States, 93% in Hong Kong, and
88% in Taiwan.
That year, 64% of the Singapore public favored mandatory wearing of
a face mask in public in the event of contagion, compared with 53% in the United
States, 86% in Hong Kong, and 96% in Taiwan.
On April 3, 2020, Singapore did
advise its citizens to wear masks in public, and announced a program for mask
Is it biologically plausible that masks might prevent transmission of infection by
blocking respiratory droplets containing the virus? Anthony S. Fauci, MD, the director of
United States National Institute of Allergy and Infectious Diseases has stated:
"The primary purpose of a face mask is to protect a healthcare worker when he or she is
taking care of somebody that’s sick. The secondary use is to get somebody who is sick
to put it on themselves to prevent them from infecting somebody else. Other people who
want to protect against getting infected in society, they can use face masks. The reason
we didn’t recommend it early on is we didn’t want the supply of face masks to be used
for people who didn’t really need it, when the physicians and the nurses and the other
healthcare providers who needed weren’t getting it. In a perfect world, if you have
enough face masks, there’s nothing wrong with wearing a face mask. Is it 100%
protective? No way. What is it? Estimate? Maybe 50% or so, and that’s merely an
estimate. There’s some degree of protection, but it isn’t completely protective against
The number of people infected on average by a virus is not a fixed number, but
depends on the circumstances. For instance, policies to social distance and close
schools and businesses can lower this value. Mask usage might provide additional
lowering of this value. A 50% reduction in transmission could be a potentially enormous
effect in an exponential process. If each infected person tends to infect 1.8 other
people (in a given environment), and masks reduce the transmission by 50%, as
estimated by Dr. Fauci, then each person infects only 0.9 other people, and exponential
growth becomes exponential decay.
Even though the final outcomes in the Western countries which recently
mandated masks are not yet known, it seems prudent to advise wearing of masks by
the public when they are anywhere near other members of the public, or close to
surfaces touched by others, such as keyboards, tables, or doorknobs. Indeed, the U.S.
CDC on April 3, 2020 issued a new guideline stating:
“CDC recommends wearing cloth face coverings in public settings where other social
distancing measures are difficult to maintain (e.g., grocery stores and pharmacies)
especially in areas of significant community-based transmission.”
This is potentially a major step forward towards control of the disease. Still, the new
guidelines should go farther. First, the current social-distancing guidelines ask people
to maintain a distance of 6 feet. If one is acting on the assumption that masks might
help reduce transmission, there is every reason to continue to wear a mask even if one
is 6 feet from one’s neighbor. Both distancing and masks can be used to lower risk
simultaneously. We have not seen evidence that the virus can travel 5 feet but not 6
feet. If our current policies (including the 6 foot spacing) were sufficient, then we would
probably not find ourselves in the middle of a pandemic. Second, the guideline does
not mention wearing a mask when near a surface touched by others, such as a table,
desk, keyboard, or groceries. Handwashing has been universally advocated because
virus particles can settle on the surfaces we touch with our hands. If a mask is worn in
public, it will block many of the respiratory droplets, and prevent them from landing on
these surfaces to begin with. Combining masks with handwashing provides the highest
level of protection. Another problem with the guideline is that really all community-
based transmission is significant. The guideline implies that in the middle of a
pandemic there could be a low-level (not “significant”) of community transmission at
which it is acceptable to fail to take minimal precautions. In fact, it is the failure to take
such basic steps which has permitted the virus to take hold in communities and expand
exponentially. Finally, the guideline is voluntary, and it may be difficult to attract public
support if important leaders fail to wear a mask themselves. Currently, a patient at the
slit lamp or a rider on a bus might falsely believe that they do not have a duty to wear a
Singh, Fauci 2020.
United States Centers for Disease Control, April 3, 2020.
mask to protect those around them. The new guideline is somewhat akin to an
automobile regulation which stated:
“We no longer want to discourage people from using headlights on their cars when
driving at night. In fact, we recommend that people voluntarily turn on the headlights at
night if their car does not have functioning turn signals, especially if they are in an area
which has had a ‘significant’ number of traffic fatalities. The guideline is voluntary, and
many of our leaders doubt that they will ever turn on their headlights.”
Thus, the guideline is a major step forwards, but it should be strengthened and
implemented more vigorously.
The guideline also does not address other personal protective equipment, such
as gloves and goggles. It may seem extreme to use a mask, gloves, and goggles, but
use of this type of equipment is certainly less extreme than closing all schools and
businesses. In fact, the manufacture, sale, and distribution of personal protective
equipment can provide jobs for many people, and can help other people return to their
During the HIV epidemic, the principle of universal precautions was emphasized.
Rather than assess an individual’s risk of having a particular disease, gloves were
required whenever drawing blood from any patient. The principle of universal
precautions with respect to the novel coronavirus requires that distancing be respected,
and masks be worn, for all encounters.
As ophthalmologists who, collectively, have backgrounds in public health and
government service, we felt compelled to study the epidemiology of COVID-19 disease.
Physicians from all specialties, especially those practicing close to the airway, have died
from COVID-19. One of the first to call attention to the novel coronavirus disease was
Li Wenliang, a Chinese ophthalmologist, who believed he acquired the disease from an
asymptomatic patient with glaucoma.
Subsequently, two more ophthalmologists in
Li’s department in Wuhan died from COVID-19. Our belief more broadly that all people
should cover their mouth and nose in public has specific application to ophthalmology.
When in the same room, but especially when at the slit lamp, droplet precautions
specify that the physician should wear a mask (and gloves) and the patient should also
wear a face covering. Slit lamps must have a breath shield.
More broadly, as citizens whose communities have been upended by this tragic
pandemic, we seek a vigorous public health response, which can save lives, and help
our communities to return to a more normal way of life.
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