COVID-19: when should quarantine be enforced?
Authors: Chris T Bauch, Madhur Anand
Journal: The Lancet Infectious Diseases (2020)

When children are little, they like to pose dilemmas as "would you rather" questions that involve difficult trade-offs. Would you rather fight an elephant-sized duck or five human-sized rhinos? Would you rather have a runny nose for a month or dry eyes? The options are not only both undesirable, but also incomparable. These questions are how we might think of some of the dilemmas created by the COVID-19 pandemic, which presents us with difficult trade-offs in equity, economics, public health, and civil liberties. In The Lancet Infectious Diseases, Corey M Peak and colleagues1Peak CM Kahn R Grad YH et al.Individual quarantine versus active monitoring of contacts for the mitigation of COVID-19: a modelling study.Lancet Infect Dis. 2020; (published online May 20.)https://doi.org/10.1016/S1473-3099(20)30361-3Summary Full Text Full Text PDF PubMed Scopus (129) Google Scholar explore one such dilemma. Plainly put, they ask the question: should health authorities place potentially exposed individuals into a quarantine setting where their separation from others can be enforced, or should authorities simply let them go home, ask them to avoid contacts, and monitor them for COVID-19 symptoms through phone calls or health-care visits? The authors name the two options individual quarantine and active monitoring, respectively. Individual quarantine impinges more on civil liberties but is less risky from a public health perspective. Aware of this dilemma, Peak and colleagues1Peak CM Kahn R Grad YH et al.Individual quarantine versus active monitoring of contacts for the mitigation of COVID-19: a modelling study.Lancet Infect Dis. 2020; (published online May 20.)https://doi.org/10.1016/S1473-3099(20)30361-3Summary Full Text Full Text PDF PubMed Scopus (129) Google Scholar use a mathematical model of the early spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections to establish the conditions under which individual quarantine works better than active monitoring. Under a broad range of model parameters the authors find that there is no difference in the effectiveness of the two strategies. They either both contain the outbreak, or they both do not contain it. However, an important exception occurs if the serial interval (time between symptom onset in an infector and their infectees) of the infection2Du Z Xu X Wu Y Wang L Cowling BJ Meyers LA The serial interval of COVID-19 from publicly reported confirmed cases.medRxiv. 2020; (published online Jan 1.) (preprint).DOI: 10.1101/2020.02.19.20025452Google Scholar is around 4·8 days, and if at least 75% of infected contacts are identified within 12 h, on average. Under those circumstances, individual quarantine could contain an outbreak, whereas active monitoring could not. This prediction appears to be consistent with another recently published model of COVID-19 containment.3Ferretti L Wymant C Kendall M et al.Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing.Science. 2020; (published online March 31.)DOI:10.1126/science.abb6936Crossref Scopus (1649) Google Scholar Crucially, this analysis assumes that testing is rapid and widely available, which is not true for many places. In view of evidence that the SARS-CoV-2 serial interval is probably about 5 days,2Du Z Xu X Wu Y Wang L Cowling BJ Meyers LA The serial interval of COVID-19 from publicly reported confirmed cases.medRxiv. 2020; (published online Jan 1.) (preprint).DOI: 10.1101/2020.02.19.20025452Google Scholar these observations raise the question: how hard is it to attain 75% success in tracing of infected contacts? This rate might be impractical with manual contact tracing, depending on the route of transmission. Interviews with individuals are stymied by problems of cognitive bias, inability of individuals to remember their detailed movements, and difficulty in identifying contacts unknown to the patient. By contrast, digital technologies offer vast improvements in terms of location accuracy and contact identification;3Ferretti L Wymant C Kendall M et al.Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing.Science. 2020; (published online March 31.)DOI:10.1126/science.abb6936Crossref Scopus (1649) Google Scholar these technologies put the 75% target within reach, as the experience of South Korea with COVID-19 has shown.4COVID-19 National Emergency Response CenterEpidemiology & Case Management TeamKorea Centers for Disease Control & PreventionContact transmission of COVID-19 in South Korea: novel investigation techniques for tracing contacts.Osong Public Health Res Perspect. 2020; 11: 60-63Crossref PubMed Scopus (135) Google Scholar However, using digital surveillance to reach the target would then present two infringements on civil liberties: individuals must be tracked to capture enough infected contacts, and those contacts must be individually quarantined. And even if contact tracing fails to contain an outbreak, the combined effect of physical distancing and contact tracing is greater than the effect of either intervention on its own.1Peak CM Kahn R Grad YH et al.Individual quarantine versus active monitoring of contacts for the mitigation of COVID-19: a modelling study.Lancet Infect Dis. 2020; (published online May 20.)https://doi.org/10.1016/S1473-3099(20)30361-3Summary Full Text Full Text PDF PubMed Scopus (129) Google Scholar Hence, the authors' analysis tells us that many decision makers will need to choose whether to use digital surveillance. Mathematical models such as those used by Peak and colleagues1Peak CM Kahn R Grad YH et al.Individual quarantine versus active monitoring of contacts for the mitigation of COVID-19: a modelling study.Lancet Infect Dis. 2020; (published online May 20.)https://doi.org/10.1016/S1473-3099(20)30361-3Summary Full Text Full Text PDF PubMed Scopus (129) Google Scholar can help decision makers to adopt an evidence-based approach to addressing the difficult dilemmas that we will continue to face during the COVID-19 pandemic. However, we suggest that mathematical models should go beyond addressing strictly epidemiological questions. The pandemic has affected almost every aspect of our individual and collective lives, and our own reactions to the pandemic shape the outbreaks we experience. Hence, we think researchers should broaden their focus to developing models that explicitly include relevant social processes, equity considerations, and economic impacts in the model structure. There is already a precedent for this approach in modelling endemic infectious diseases5Bauch CT Galvani AP Social factors in epidemiology.Science. 2013; 342: 47-49Crossref PubMed Scopus (167) Google Scholar, 6Bonds MH Keenan DC Rohani P Sachs JD Poverty trap formed by the ecology of infectious diseases.Proc Biol Sci. 2010; 277: 1185-1192Crossref PubMed Scopus (142) Google Scholar and in other fields of natural systems modelling.7Innes C Anand M Bauch CT The impact of human–environment interactions on the stability of forest-grassland mosaic ecosystems.Sci Rep. 2013; 32689Crossref PubMed Scopus (60) Google Scholar On a final note, we speculate that the COVID-19 quarantine and monitoring dilemma is in some ways not as difficult to address as the "would you rather" questions of children. Contact tracing represents a race to trace.8Kaplan EH Craft DL Wein LM Emergency response to a smallpox attack: the case for mass vaccination.Proc Natl Acad Sci USA. 2002; 99: 10935-10940Crossref PubMed Scopus (308) Google Scholar To prevent exponential growth in the number of cases, public health must trace contacts of infected cases and reduce their chances of causing further spread faster than the virus propagates through the network of personal contacts. Thus, intrusive action in the early stages of a pandemic might reduce how much longer those intrusive measures have to be applied, and to how many people. Additionally, benefits for other fundamental rights are accrued as the pandemic unfolds, such as saving both lives and livelihoods.9United NationsThe Universal Declaration of Human Rights.https://www.un.org/en/universal-declaration-human-rights/Date accessed: April 22, 2020Google Scholar We declare no competing interests. Individual quarantine versus active monitoring of contacts for the mitigation of COVID-19: a modelling studyOur model highlights the urgent need for more data on the serial interval and the extent of presymptomatic transmission to make data-driven policy decisions regarding the cost–benefit comparisons of individual quarantine versus active monitoring of contacts. To the extent that these interventions can be implemented, they can help mitigate the spread of SARS-CoV-2. Full-Text PDF