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Public Health and Primary Care Original Article
Hadie Islam*, BS, Amina Islam, Alan Brook, MD and Mohan Rudrappa, MD
Evaluating the effectiveness of countywide mask
mandates at reducing SARS-CoV-2 infection in the
United States
https://doi.org/10.1515/jom-2021-0214
Received August 27, 2021; accepted December 13, 2021;
published online January 27, 2022
Abstract
Context: With the rise of the Delta variant of SARS-CoV-2
and the low vaccination rates in the United States, miti-
gation strategies to reduce the spread of SARS-CoV-2 are
essential for protecting the health of the general public and
reducing strain on healthcare facilities. This study com-
pares US counties with and without mask mandates and
determines if the mandates are associated with reduced
daily COVID-19 infection. US counties have debated
whether masks effectively decrease COVID-19 cases, and
political pressures have prevented some counties from
passing mask mandates. This article investigates the utility
of mask mandates in small US counties.
Objectives: This study aims to analyze the effectiveness
of mask mandates in small US counties and places
where the population density may not be as high as in
larger urban counties and to determine the efficacy of
countywide mask mandates in reducing daily COVID-19
infection.
Methods: The counties studied were those with pop-
ulations between 40,000 and 105,000 in states that did
nothavestatewidemaskmandates.Atotalof38counties
were utilized in the study, half with and half without
mask mandates. Test counties were followed for 30 days
after implementing their mask mandate, and daily
new SARS-CoV-2 infection was recorded during this
timeframe. The counties were in four randomly selected
states that did not have statewide mask mandates. The
controls utilized were from counties with similar pop-
ulations to the test counties and were within the same
state as the test county. Controls were followed for the
same 30 days as their respective test county. Data were
analyzed utilizing t-test and difference-in-difference
analyses comparing counties with mask mandates and
those without.
Results: These data showed statistically significant lower
averages of SARS-CoV-2 daily infection in counties that passed
mask mandates when compared with counties that did not.
The difference-in-difference analysis revealed a 16.9% reduc-
tion in predicted COVID-19 cases at the end of 30 days.
Conclusions: These data support the effectiveness of mask
mandates in reducing SARS-CoV-2 infection spread in
small US counties where the population density may be
less than in urban counties. Small US counties that are
considering passing mask mandates for the population can
utilize these data to justify their policy considerations.
Keywords: COVID-19; infection; mask mandate; pandemic;
public health; SARS-CoV-2.
Since its first appearance in Wuhan, China in December
2019, the novel coronavirus designated as SARS-CoV-2 has
infected over 240 million people, and it has caused about
4.9 million deaths worldwide as of October 2021 [1]. This
pandemic has crippled the global economy and has had
numerous detrimental effects on societies [2]. The optimal
measure to contain this pandemic has varied from nation to
nation [3]. For example, the use of mask mandates in the
developed world has been a contested topic [4]. Although
vaccinations are now available in the United States, many
people have been hesitant to receive the vaccine out of
safety concerns, largely due to misinformation about the
vaccines [5]. It is essential for public health experts and
local county officials to implement strategies to reduce
COVID-19 spread to protect the health of the general pop-
ulation and to reduce the strain on health providers. Our
study aims to investigate the utility of mask mandates in
*Corresponding author: Hadie Islam, BS, College of Osteopathic
Medicine, Kansas City University, 2901 St. John’s Boulevard, Joplin,
MO 64804, USA, E-mail: hadieislam@kansascity.edu
Amina Islam, School of Medicine, University of Missouri Kansas City,
Kansas City, MO, USA
Alan Brook, MD, Internal Medicine/Pulmonology, Barnes Jewish
Hospital, St. Peters, MO, USA
Mohan Rudrappa, MD, Internal Medicine/Pulmonology, Mercy
Hospital, Joplin, MO, USA
J Osteopath Med 2022; 122(4): 211–215
Open Access. © 2022 Hadie Islam et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0
International License.
small US counties and to determine if mask mandates
effectively reduce SARS-CoV-2 transmission.
SARS-CoV-2 is a positive-sense RNA virus primarily
transmitted through contact with respiratory droplets
and infected humans, but it can also be transmitted
through contaminated surfaces [6]. A steadily growing
number of observational and epidemiologic studies have
shown statistically significant evidence that the use of
face masks reduces SARS-CoV-2 transmission [7]. One
study shows that the Hong Kong Special Administrative
Region (HKSAR), where an estimated 96.6% of the
observed public wore face masks, had a significantly
lower incidence of COVID-19 cases per million population
between December 31, 2019 and April 8, 2020 compared to
nations without universally adopted face mask usage.
For reference, the population of HKSAR is approximately
7.45 million people [8]. In another study, there was no risk
of transmission from two infected hairstylists and nearly
139 clients, of which the mean age was 52 years old (age
range, 21–93 years), and this was attributed to the use of
masks [9]. Furthermore, evaluation of 382 sailors (inter-
quartile age range, 24–35 years) on the USS Theodore
Roosevelt, a US navy ship, found that those who took
extra precautions to prevent SARS-CoV-2 infection, such
as mask-wearing, had a 70.0% reduction in transmission
when compared to those who did not wear masks [10].
Another study looking at 15 US states (plus Washington,
D.C.) with mandated mask requirements found a 2.0%
decline in the daily SARS-CoV-2 growth rate after 21 days
of having passed the mask mandate [11]. In Bangladesh,
villages that adopted masking as a preventative measure
against COVID-19 found an 11.2% overall risk reduction
and a 34.7% risk reduction for people older than 60 years
old in becoming infected with the virus [12]. A recent
study showed that US states that had mask mandates had
a 0.5% decrease in daily COVID-19 infections, as well as a
0.7% decrease in daily COVID-19 deaths compared to
when those states did not have mask mandates [13].
Based on current evidence, it is reasonable to conclude
that masking reduces the transmission of SARS-CoV-2
effectively. As stated earlier, masks may limit the spread
of respiratory droplets; however, it is important to note
that additional protective actions, such as hand washing
and physical distancing, are also thought to play a role in
reducing SARS-CoV-2 transmission [14]. In the United
States, the mandated use of masks has been variable
despite the CDC recommendations. In 2020, only 38 states
and the District of Columbia (DC) issued mandates [13].
Our study aims to determine the difference in the
incidence of new infections after mandating face mask
use for the public.
Methods
Institutional Review Board approval was not required for this study,
because it did not collect individual patient data, and informed
consent was not necessary, because all information accessed is
publicly available. No funding was obtained for this study. The
counties included are those with populations between 40,000 and
105,000 individuals. The purpose of this population limit was due
to the lack of control samples for populations with over 105,000
individuals, because nearly all of these counties had mask mandates
in effect during preliminary analysis. Counties with less than 40,000
individuals were excluded because smaller counties tended not to
have enough dail y infections to analyze. D ata were gathered utilizin g
the US Census Bureau’s 2019 population est imates [15]. Demographic
data were also found utilizing the US Census Bureau’s data [16]. The
demographic information recorded includes the total estimated
population and the average age of the test and control counties.
Whether or not a county had a mask mandate was determined
utilizing local, online news reports announcing the start times of the
mandates. States excluded from the study were those with statewide
mask mandates as of August 17, 2020. Four states were randomly
selected from a pool of states without mask mandates. This was done
by assigning each state without a mask mandate a number and then
selecting the four states via Microsoft Excel’s random number
generator function (Version 2018). Missouri, Iowa, Tennessee, and
Florida were the four states chosen via this selection process.
Counties within these states that met the inclusion criteria and
had a mask mandate were labeled as test counties. If a county was
within the same state as the test county, had a similar population
within 10,000 people, and did not have a mask mandate, this county
would be labeled as a control county (Table 1). Each test county’s
SARS-CoV-2 daily infection rates were followed for 30 days after the
start date of their mask mandate, as well as for 10 days before the
mandate. If a county had multiple times that a mask mandate was
passed, the first time the mask mandate was passed was utilized for
data analysis. The selected control counties were observed for the
same 30 days after and 10 days before the test county’s mask mandate.
Daily COVID-19 transmission data per county were collected utilizing
USAfacts.org [17].
Statistical analysis was performed via a two-tailed, unpaired
t-test comparing new daily SARS-CoV-2 infections of the test counties
and control counties. A p value <0.05 will be considered statistically
significant.To further evaluate the effectiveness of mask mandates,
difference-in-difference analysis was performed comparing test
counties and control counties 10 days before the mask mandate vs.
30 days after the mandate. This was done to show the trend of
COVID-19 infections before and after the mask mandates. Statistical
software utilized was SPSS (Version 28.0.0.0). A total of 19 counties
that met the inclusion criteria were found to have mask mandates,
and 19 controls were also selected utilizing the requirements listed
above.
212 Islam et al.: Evaluating the effectiveness of countywide mask mandates
Results
The average population for the test counties was 71,316,
and the control county average was 72,158 (p=0.89). The
average age for the test counties was 40.5 years old, and the
average age for the control counties was 41.8 (p=0.37). Data
were collected from July 2020 to October 2020.
After following each county for 30 days after mask
mandates were passed, the test counties had an average of
19.63 new COVID-19 infections per day, and the control
counties had an average of 23.34 new COVID-19 infections per
day. T-test analysis revealed a p value of 0.009 (Figure 1).
Difference-in-difference analysis revealed that test
counties had a similar average COVID-19 case rate 10 days
before the mask mandate was passed compared to the
controls (16.05 average cases and 14.01 average cases,
respectively). After 30 days of the mask mandate, the test
counties had a lower average of COVID-19 cases than the
controls. The average treatment effect reduced COVID-19
cases by 4.22 cases per day, or 16.9% when utilizing the
difference-in-difference analysis (p=0.01) (Figure 2).
Discussion
Mask mandates to prevent the spread of SARS-CoV-2
transmission are controversial primarily due to political
pressures. Prior studies and thisstudy suggest that masking
is effective at reducing SARS-CoV-2 transmission. This study
evaluated mask mandates in small US counties to determine
their effectiveness in regions where populations may not be
as densely packed. Based on our preliminary findings,
smaller counties were less likely to pass mask mandates to
reduce the spread of COVID-19 [18]. The purpose of this
study was to evaluate the utility and effectiveness of mask
mandates in small counties. Based on our results, counties
that passed mask mandates showed significantly lower
average daily COVID-19 transmission rates when compared
to other similar counties in the states that did not pass mask
mandates. Our data also show that test counties had a lower
incidence rate of COVID-19 cases than controls. The differ-
ences between the population and age in test counties, and
the population and age in control counties, were not sta-
tistically significant, indicating that the populations of the
control counties are similar to the populations of the test
counties. With these data, we conclude that mask mandates
reduce SARS-CoV-2 transmission among the general popu-
lation. Physicians who live in communities with low mask
compliance can utilize these data to inform patients of the
ability of masks to reduce the risk of SARS-CoV-2 infection.
They can also utilize these data to pressure local govern-
ment officials to mandate mask use in public spaces. With
the rise of the Delta variant of SARS-CoV-2 in the United
States and the relatively low vaccination rate among the
population both in the United States and globally, it is
essentialto utilize multiple methods to reduce the spread of
Table :The demographic data from each county evaluated.
Test counties
County name Population Average age, years
Cape Girardeau County, MO , .
Christian County, MO , .
Johnson County, MO , .
Platte County, MO , .
St. Francois County, MO , .
Story County, IA , .
Carter County, TN , .
Fayette County, TN , .
Greene County, TN ,
Hamblen County, TN , .
Hawkins County, TN , .
Madison County, TN , .
Robertson County, TN , .
Sevier County, TN , .
Tipton County, TN , .
Warren County, TN ,
Gadsden County, FL , .
Monroe County, FL , .
Nassau County, FL , .
Average county stats , .
Control counties
County name Population Average age, years
Cole County, MO , .
Buchanan County, MO , .
Lincoln County, MO , .
Cass County, MO , .
Newton County, MO , .
Dubuque County, IA , .
Coffee County, TN , .
Cheatham County, TN , .
Anderson County TN , .
Putnam County TN , .
Cumberland County, TN ,
Maury County, TN ,
Putnam County TN , .
Maury County, TN ,
Cumberland County, TN ,
Loudon County, TN , .
Jackson County, FL , .
Walton County FL , .
Putnam County FL , .
Average county stats , .
Islam et al.: Evaluating the effectiveness of countywide mask mandates 213
COVID-19. The data analyzed in this study suggest that mask
mandates are a simple yet effective way to reduce trans-
mission of the SARS-CoV-2 virus.
Our study did have some limitations. We did not record
compliance with mask mandates and did not actively
pursue other factors known to prevent virus spread, such
as lockdowns and social distancing. Nevertheless, our
study reinforces the CDC guidelines regarding the efficacy
of face masks in controlling the spread of the SARS-CoV-2
pandemic.
Figure 2: Daily COVID-19 cases in test counties vs. control counties 10 days before the mask mandate was passed and 30 days after the mask
mandate was passed.
Figure 1: The 30-day average COVID-19 cases of counties with and without mask mandates.
214 Islam et al.: Evaluating the effectiveness of countywide mask mandates
Conclusions
The use of mask mandates among the general population has
been shown to reduce the incidence of SARS-CoV-2 infection.
Masking is an effective public health measure that local
governments can implement to mitigate SARS-CoV-2 infec-
tion. In small US counties where the population density is less
than it is in larger urban areas, mask mandates still appear to
be effective at reducing COVID-19 transmission. Public health
officials and local governments can utilize these data to
provide further evidence on the effectiveness of mask man-
dates and guide their decision-making regarding passing
local mandates. With the 5 model approach to osteopathic
holistic medical practice, the behavioral model is an impor-
tant aspect of patient care. Osteopathic physicians can utilize
these data to encourage and support mask use among their
patients in the United States and abroad to help reduce
COVID-19 transmission. In future pandemics with respiratory
transmission, these data can also be utilized by physicians to
be proactive about changing the behaviors of patients and
encouraging mask use, thereby incorporating a holistic and
evidence-based approach to preventative care.
Research funding: None reported.
Author contributions: All authors provided substantial
contributions to conception and design, acquisition of
data, or analysis and interpretation of data; all authors
drafted the article or revised it critically for important
intellectual content; all authors gave final approval of the
version of the article to be published; and all authors agree
to be accountable for allaspects of the work in ensuring that
questions related to the accuracy or integrity of any part of
the work are appropriately investigated and resolved.
Competing interests: None reported.
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Islam et al.: Evaluating the effectiveness of countywide mask mandates 215
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