Modeling the Comparative Impact of Individual Quarantine vs. Active Monitoring of Contacts for the Mitigation of COVID-19

Individual quarantine and active monitoring of contacts are core disease control strategies, particularly for emerging infectious diseases such as Coronavirus Disease 2019 (COVID-19). To estimate the comparative efficacy of these interventions to control COVID-19, we fit a stochastic branching model, comparing two sets of reported parameters for the dynamics of the disease. Our results suggest that individual quarantine may contain an outbreak of COVID-19 with a short serial interval (4.8 days) only in settings with high intervention performance where at least three-quarters of infected contacts are individually quarantined. However, in settings where this performance is unrealistically high and the outbreak of COVID-19 continues to grow, so too will the burden of the number of contacts traced for active monitoring or quarantine. In such circumstances where resources are prioritized for scalable interventions such as social distancing, we show active monitoring or individual quarantine of high-risk contacts can contribute synergistically to social distancing. To the extent that interventions based on contact tracing can be implemented, therefore, they can help mitigate the spread of COVID-19. Our model highlights the urgent need for more data on the serial interval and the extent of presymptomatic transmission in order to make data-driven policy decisions regarding the cost-benefit comparisons of individual quarantine vs. active monitoring of contacts. 1 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted March 8, 2020. ; https://doi.org/10.1101/2020.03.05.20031088 doi: medRxiv preprint NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice. Introduction In December 2019, Coronavirus Disease (COVID-19) emerged in Wuhan, China.​ 1​ It has since spread globally, reaching more than three dozen countries with over 80,000 confirmed cases by late February.​ 2​ To reduce further spread of the disease, governments have implemented community measures to increase social distancing for those at highest risk of infection.​ 3​ In China, policies include unprecedented lockdowns to reduce contacts between individuals, travel restrictions, and door-to-door temperature checks with mandatory mass quarantine.​ 4 Contact tracing, a core strategy to control disease, is used to identify individuals who may have been exposed to an infectious disease and to focus interventions on this high risk group. If identified contacts are symptomatic when found, they are promptly isolated and treated in a healthcare setting. More often, contacts are found healthy, and may or may not be infected. Depending on how much time has passed since exposure to the primary infected individual, those infected may not yet be symptomatic this period of time between infection and symptoms is an important epidemiological trait of an infectious disease called the incubation period. How to handle these symptom-free contacts is a recurring point of confusion and controversy, particularly for emerging infectious diseases. Two essential strategies are used: individual quarantine and active monitoring. Individual quarantine involves the separation from others of an individual who is believed to be exposed to the disease, but not currently showing symptoms of it. A less restrictive intervention, active monitoring, involves assessing the individual for symptoms at regular intervals and, if symptoms are detected, promptly isolating the individual. The relationship between symptoms of a disease and infectiousness to others is critical to the success of containment strategies. Previous work has found that a disease’s natural history, particularly the amount of transmission that occurs before symptom onset, greatly influences the ability to control outbreaks​ 5​ ​and the relative effectiveness of individual quarantine vs. active monitoring.​ 6​ Short-course diseases, such as influenza, and diseases with long periods of presymptomatic infectiousness, like hepatitis A, are impacted more strongly by quarantine than by active monitoring; however, quarantine is of limited benefit over active monitoring for the coronaviruses MERS and SARS, where persons usually show distinctive symptoms at or near the same time that they become infectious. Recent work on isolation for COVID-19 found a potentially large impact of perfect isolation, if one assumed there was limited presymptomatic transmission and a high probability of tracing contacts to be put under isolation immediately following symptom onset.​ 7​ Our framework enables comparison of active monitoring and individual quarantine and considers parameters such as delays, and imperfect isolation to account for known nosocomial transmission of this respiratory virus.​ 8 One of the key uncertainties surrounding COVID-19 is the extent of asymptomatic and presymptomatic transmission. A recent study reporting asymptomatic transmission in Germany​ 9 was later found to be incorrect or misleading,​ 10​ ​adding to the confusion. There has also been uncertainty about the serial interval the time between symptom onset of infector-infectee pairs which in turn reflects uncertainty about the extent of presymptomatic transmission. Early 2 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted March 8, 2020. ; https://doi.org/10.1101/2020.03.05.20031088 doi: medRxiv preprint