The University of Tennessee, Knoxville.
Social Distancing: How it Works and Why it Matters
A Policy Brief by the Howard H. Baker Jr. Center for Public Policy
in Partnership with the Coronavirus-19 Outbreak Response Experts (CORE-19)
April 13, 2020
Tennessee State Capitol and Flag
Using publicly available data from emerging research on COVID-19, this brief was written and reviewed by the Coronavirus-19 Outbreak Response Experts (CORE-19) at the University of Tennessee, Knoxville. It explains the merits of social distancing and discusses the optimal duration for sustained success. 

Social Distancing: How it Works and Why it Matters

When confronting a novel virus like COVID-19, suppression policy and community mitigation strategies are critical to protecting the health of Americans and preventing excess economic hardship. Especially in the absence of a cure or vaccination, which experts agree will not become widely available for at least 12 to 18 months, non-pharmaceutical interventions (commonly referred to as Social Distancing) are often the only way to combat the harmful impact of a pandemic outbreak in real-time.
Recent debate among some policymakers is raising the question about whether large-scale mitigation and suppression policies through individual behaviors and public policy may impose greater long-term economic costs than simply allowing day-to-day economic activity to proceed.
However, a recent cost-benefit analysis estimates that absent extensive suppression policies the economic cost of COVID-19 could total over $9 trillion and 1.3 million fatalities. Thus, action is required to prevent potentially extraordinary economic and social costs.
The economic cost of COVID-19 could total over $9 trillion and 1.3 fatalities. 
This policy brief provides insight into the costs associated with public health interventions and reviews the emerging evidence about the effectiveness and optimal duration of public policy interventions. 

Social Distancing and Non-Pharmaceutical Interventions

According to the Centers for Disease Control and Prevention (CDC), non-pharmaceutical interventions and community mitigation strategies, such as ‘Stay at home’ orders and the closure of schools and businesses, have three distinct goals:
  1. Slow the acceleration of the number of cases in a community, which allows more time for the development, distribution, and administration of a pandemic treatment or vaccination.  

  2. Reduce the peak number of cases during the pandemic and related health care demands on hospitals and infrastructure, helping to prevent healthcare systems from reaching maximum capacity and thereby preserving the quality and availability of medical care

  3. Decrease overall cases and health effects by reducing disease transmission, which in turn can reduce morbidity and mortality.
In essence, mitigation and suppression policies, combined with personal protection measures, are intended to artificially reduce the basic reproduction number (R0) – the average number of people an infected person infects assuming the population has no existing immunity – for a disease. 
These measures are particularly important for combatting COVID-19, given that conservative estimates of the R0 for COVID-19 are exceedingly higher than the seasonal flu and limited evidence suggests asymptomatic carriers may play a significant role in the transmission of the virus.

Suppression Versus Mitigation

Non-pharmaceutical interventions and personal protective strategies in response to a pandemic outbreak, such as COVID-19, are classified in two ways:
  1. Mitigation – policies aimed at slowing disease transmission but not stopping it altogether (e.g. social distancing, hand hygiene, routine cleaning of surfaces, etc.)
  2. Suppression – policies aimed at reversing epidemic growth altogether for an extended period of time (e.g. ‘stay at home’ orders, school closures, telecommuting, etc.) 
The primary difference between mitigation and suppression is that suppression policy must be maintained for a large extent of an outbreak, whereas mitigation relies on a population slowly developing immunity throughout the epidemic.
However, to be successful, mitigation strategies rely on the assumption that individuals will not become re-infected for a significant period of time following the original infection (Limited evidence based on previous seasonal coronaviruses suggests re-infection in the short-term is unlikely). 
According to a recent 2020 report published by the Imperial College COVID-19 Response Team, optimal mitigation policies (e.g. self-quarantine of confirmed cases and social distancing of at-risk populations) bear the potential to reduce fatalities by 50% and peak healthcare demand by nearly 65%.
In other words, mitigation policy and behaviors can have a substantive impact on the potential control of a pandemic. However, the authors also note mitigation policies alone can still result in “hundreds of thousands of deaths” and situations where demand for medical care greatly exceeds the existing capacity
This leaves suppression as the optimal public policy approach for addressing the COVID-19 pandemic outbreak. 

Do Social Distancing and Non-Pharmaceutical Interventions Work?

Community Mitigation Guidelines to Prevent Pandemic Influenza released by the CDC in 2017 outline a range of recommended community NPIs and evidence about their effectiveness:
School Closures
  • A study from the United States analyzing the 2009 H1N1 pandemic found school closure was associated with a 45%-75% reduction in acute respiratory illness in households with school-aged children.
  • Mathematical models from the 2009 H1N1 outbreak in Canada estimate school closures reduced transmission by approximately 50% among school children.
  • During the 2009 H1N1 outbreak in Mexico City, Mexico, overall virus transmission decreased by an estimated 29%-37% after school closures and the implementation of other social distancing measures.
  • Early analysis of the COVID-19 outbreak in China shows that mass school closures can “achieve a noticeable decrease in infection attack rate and peak incidence.”
Use of Face Masks in Community Settings
  • A systematic review of nine articles found that “face mask use alone and face mask use with hand hygiene may prevent infection in community settings,” especially when implemented early and with wide-spread compliance.
Telecommuting and Cancellation of Mass Gatherings
Lockdowns and 'Stay at Home' Orders
'Stay at Home' orders in the United States are the most effective intervention for reducing R0 - the number of people an infected person infects - in terms of magnitude.
More broadly, a recent report published by the Imperial College COVID-19 Response Team, evaluating the effectiveness of non-pharmaceutical interventions in 11 European countries, finds that multiple NPIs implemented synchronously have already had a “substantial impact on transmission,” lowering the effective basic reproduction number (R0) by an estimated 64% compared to the natural R0 for COVID-19
Figure (2) below displays sensitivity analysis from the Imperial College COVID-19 Response Team comparing the relative effectiveness of individual NPIs in reducing the R0 for COVID-19:
It is also important to note that, given state government autonomy in the United States, public policy measures in bordering states and cross-state contact may impact the effectiveness of NPIs. This mean policy coordination among states is integral to achieving an optimal outcome.
Overall, a wealth of evidence suggests that personal protective measures and non-pharmaceutical interventions (e.g. suppression and mitigation policy) limit disease transmission, lower peak death rates, and reduce overall mortality.

Optimal Duration: Is a Cure Worse than the Disease?

A recently published working paper by Anna Scherbina, a former Senior Economist at the White House’s Council of Economic Advisors, seeks to address this question directly, modeling the COVID-19 outbreak based on its basic reproduction number (R0) – the average number of people an infected person infects assuming the population has no existing immunity – and comparing the weekly incremental economic cost of suppression measures relative to the economic cost imposed by the virus (e.g. fatalities, medical costs, and decreased labor productivity)
The optimal duration for suppression policy is ascertained by balancing the weekly costs and benefits of suppression policy, and the point at which suppression policy should be lifted, in favor of mitigation policy, is when the weekly cost begins to exceed the weekly benefit.
Affirming  similar findings noted by the CDC, the study suggests the optimal duration of suppression policy “crucially depends on the policy’s effectiveness in reducing the rate of the virus transmission.”
Lifting suppression policies prematurely can lead to a resurgence in infection rates that would further weaken the economy and potentially lead to the enactment or re-enactment of more stringent policies. 
To build the cost-benefit analysis model, the author works from the baseline scenario that suppression policy will be in place for the next 4 weeks and makes the following assumptions about the nature of COVID-19:
  • Basic reproduction number (R0) is 2.4
  • Infection fatality ratio (IFR) is 0.74%
  • Vaccine becomes available in 18 months
  • Risk profile and medical costs are similar to the seasonal influenza
  • Only 60% of the population is symptomatic
  • Only 50% of cases are diagnosed
  • Diagnosed and undiagnosed illnesses amount to 1 million cumulative cases
It is important to note that these are well-founded assumptions, but they are assumptions nonetheless and initial evidence suggests these metrics may vary by region and locality. COVID-19 could, for example, be more contagious than the model assumes with an R0 value of 2.24.
Based on data from 11 European countries, the Imperial College COVID-19 Response Team estimated the R0 for COVID-19 is between 3.01 and 4.66, and the CDC recently revised its initial estimate, finding a median R0 value of 5.7 for COVID-19. Likewise, more than the assumed 60% of the infected population may become symptomatic, as one study from the National Institutes of Health estimates the asymptomatic proportion is between 15.5% and 20.2% of cases.
Figure (3) below shows a scenario where suppression policy is moderately successful (assuming R0 is artificially reduced from 2.24 to 0.7), thus suppression should be replaced with mitigation after 17 weeks:
R0 = 0.7 (Net savings from suppression: $3.68 trillion)
Figure (4) below shows a scenario where suppression policy is very successful (assuming R0 is artificially reduced from 2.24 to 0.5), thus suppression should be replaced with mitigation after 9 weeks:
R0 = 0.5 (Net savings from suppression: $3.73 trillion)
Additionally, the paper finds that “stopping the suppression policy before six weeks [would] not produce any meaningful improvements in the pandemic outcome.” This finding aligns with CDC guidance warning that “premature discontinuation of NPIs” may fail to achieve significant reductions in attack rates and “risk reintroduction of the virus.”
Evidence suggests extending suppression policy, at least in the short term, is the only plausible way to reduce disease transmission and ultimately mortality. While it might seem counterintuitive, Tennesseans may be better off economically if suppression policy is extended and unessential businesses remained closed for the time being.
Another study, which uses a mathematical model of COVID-19 based on data from the COVID-19 outbreak in South Korea, finds that the “most effective interval for imposing a limited-duration lockdown is one which straddles the peak of the spread of the disease in society in the absence of the lockdown.”
Additionally, they find that the trajectory of reported cases may not reflect the impact of suppression in real-time, even when the suppression policy was well-timed and significantly slowed disease transmission.
Even after weighing the enormous costs suppression policy imposes on the economy, clear and compelling evidence exists that shows lifting suppression policy prematurely, or failure to act altogether, would impose an even greater cost to the Tennessee and United States economy.

Importance of Compliance

Compliance and enforcement are central to the effectiveness of suppression and mitigation policy. A recent study modeling the transmission and control of COVID-19 in Australia found that suppression policy and social distancing with a level of compliance below 70% is unlikely to have a substantive effect.
However, coupled with case isolation and international travel restrictions, the authors find suppression policy compliance at the 90% level can contain the disease within 13-14 weeks, but the model does not consider the potential reintroduction of the virus once interventions are relaxed.
One model shows how compliance with the suppression policy might impact the COVID-19 outbreak specifically in Tennessee:
“Stay at home (lax)” reflects a 50% contact rate reduction, whereas “Stay at home (strict)” reflects a 70% contact rate reduction. This suggests a 20% percentage point difference in compliance (or reduced effective contact) could reduce estimated deaths by 24,000. Put simply, broad and robust community compliance can both shorten the optimal duration of suppression policy and result in fewer deaths.
The evidence presented here suggests layered non-pharmaceutical interventions (NPIs) and social distancing measures, significant in scope and duration, are the most effective policy option available to combat COVID-19.
Especially when no cure or vaccination is available, proactive interventions with broad community compliance can meaningfully alter the health and economic impact of COVID-19.
Hancen Sale

Hancen Sale

Hancen Sale is an undergraduate researcher  with the Center. He is a senior majoring in economics with a minor from the Center's public policy analytics program. He has worked on an NSF-funded project regarding rebel group grievances, as well as in supporting The White House's American Workforce Policy Advisory Board. 
Dr. Kathleen Brown

Dr. Kathleen C. Brown, PhD, MPH

Brown is an Associate Professor of Practice in the Department of Public Health and the Program Director for the Master's in Public Health (MPH) degree. Her research focuses on the health and well-being of individuals and communities. She has experience in local public health in epidemiology, risk reduction and health promotion.
Dr. Katie Cahill

Dr. Katie A. Cahill, PhD

Cahill is the Associate Director of the Howard H. Baker Jr. Center for Public Policy. She also is the Director of the Center's Leadership & Governance program and holds a courtesy faculty position in the Department of Political Science. Her area of expertise is public health policy. She leads the Healthy Appalachia project. 
Dr. Kristina Kintziger

Dr. Kristina W. Kintziger, PhD, MPH

Kintziger is an Assistant Professor in the Department of Public Health and the co-Director of the Doctoral Program. She has worked in academia and public health practice, and comes to Tennessee from the Florida Department of Health, where she worked as an epidemiologist and biostatistician. She is an environmental and infectious disease epidemiologist.
Dr. Matthew Murray

Dr. Matthew N. Murray, PhD

Murray is the Director of the Howard H. Baker Jr. Center for Public Policy. He also is the Associate Director of the Boyd Center for Business and Economic Research and is a professor in the Department of Economics in the Haslam College of Business. He has led the team producing Tennessee's annual economic report to the governor since 1995. 
Dr. Agricola Odoi

Dr. Agricola Odoi, BVM, MSc, PhD

Odoi is a professor of epidemiology at the University of Tennessee College of Veterinary Medicine. He teaches quantitative and geographical epidemiology and his research interests are in population health and impact of place on health and access to health services. He was a public health epidemiologist before joining academia.
Dr. Marcy Souza

Dr. Marcy J. Souza, DVM, MPH

Souza is an associate professor and Director of Veterinary Public Health in the UT College of Veterinary Medicine.  Her teaching and research focuses on zoonotic diseases and food safety issues. 
Disclaimer: the information in this policy brief was produced by researchers, not medical or public health professionals, and is based on their best assessment of the existing knowledge and data available on the topic. It does not constitute medical advice and is subject to change as additional information becomes available. The information contained in this brief is for informational purposes only. No material in this brief is intended to be a substitute for professional medical advice, diagnosis or treatment, and the University of Tennessee makes no warranties, expressed or implied, regarding errors or omissions and assumes no legal liability or responsibility whatsoever for loss or damage resulting from the use of information provided.
Howard H. Baker Jr Center for Public Policy
1640 Cumberland Avenue
Knoxville, TN 37996
Phone: 865-974-0931
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