Quarantine and testing strategies in contact tracing for SARS-CoV-2: a modelling study

Centre for the Mathematical Modelling of Infectious Diseases COVID-19 working group

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23 Citations (Scopus)

Abstract

Background: In most countries, contacts of confirmed COVID-19 cases are asked to quarantine for 14 days after exposure to limit asymptomatic onward transmission. While theoretically effective, this policy places a substantial social and economic burden on both the individual and wider society, which might result in low adherence and reduced policy effectiveness. We aimed to assess the merit of testing contacts to avert onward transmission and to replace or reduce the length of quarantine for uninfected contacts. Methods: We used an agent-based model to simulate the viral load dynamics of exposed contacts, and their potential for onward transmission in different quarantine and testing strategies. We compared the performance of quarantines of differing durations, testing with either PCR or lateral flow antigen (LFA) tests at the end of quarantine, and daily LFA testing without quarantine, against the current 14-day quarantine strategy. We also investigated the effect of contact tracing delays and adherence to both quarantine and self-isolation on the effectiveness of each strategy. Findings: Assuming moderate levels of adherence to quarantine and self-isolation, self-isolation on symptom onset alone can prevent 37% (95% uncertainty interval [UI] 12–56) of onward transmission potential from secondary cases. 14 days of post-exposure quarantine reduces transmission by 59% (95% UI 28–79). Quarantine with release after a negative PCR test 7 days after exposure might avert a similar proportion (54%, 95% UI 31–81; risk ratio [RR] 0·94, 95% UI 0·62–1·24) to that of the 14-day quarantine period, as would quarantine with a negative LFA test 7 days after exposure (50%, 95% UI 28–77; RR 0·88, 0·66–1·11) or daily testing without quarantine for 5 days after tracing (50%, 95% UI 23–81; RR 0·88, 0·60–1·43) if all tests are returned negative. A stronger effect might be possible if individuals isolate more strictly after a positive test and if contacts can be notified faster. Interpretation: Testing might allow for a substantial reduction in the length of, or replacement of, quarantine with a small excess in transmission risk. Decreasing test and trace delays and increasing adherence will further increase the effectiveness of these strategies. Further research is required to empirically evaluate the potential costs (increased transmission risk, false reassurance) and benefits (reduction in the burden of quarantine, increased adherence) of such strategies before adoption as policy. Funding: National Institute for Health Research, UK Research and Innovation, Wellcome Trust, EU Horizon 2021, and the Bill & Melinda Gates Foundation.

Original languageEnglish
Pages (from-to)e175-e183
JournalThe Lancet Public Health
Volume6
Issue number3
DOIs
Publication statusPublished - Mar 2021

Bibliographical note

Funding Information:
This research was partly funded by the UK National Institute for Health Research (NIHR). BJQ is funded by NIHR grants 16/137/109 and 16/136/46 from the UK Government to support global health research. The views expressed in this publication are those of the authors and not necessarily those of the NIHR or the UK Department of Health and Social Care. BJQ is also supported in part by a grant from the Bill & Melinda Gates Foundation (OPP1139859). This research was also funded by UK Research and Innovation (grant MC_PC_19065 to SC and WJE), and partly funded by the Wellcome Trust (Sir Henry Dale Fellowship, grant 208812/Z/17/Z to SF and SC; grant 206250/Z/17/Z to AJK and TWR; and grant 210758/Z/18/Z to JH). This project received funding from the EU's Horizon 2020 research and innovation programme (project EpiPose to WJE).

Funding Information:
This research was partly funded by the UK National Institute for Health Research (NIHR). BJQ is funded by NIHR grants 16/137/109 and 16/136/46 from the UK Government to support global health research. The views expressed in this publication are those of the authors and not necessarily those of the NIHR or the UK Department of Health and Social Care. BJQ is also supported in part by a grant from the Bill & Melinda Gates Foundation (OPP1139859). This research was also funded by UK Research and Innovation (grant MC_PC_19065 to SC and WJE), and partly funded by the Wellcome Trust (Sir Henry Dale Fellowship, grant 208812/Z/17/Z to SF and SC; grant 206250/Z/17/Z to AJK and TWR; and grant 210758/Z/18/Z to JH). This project received funding from the EU's Horizon 2020 research and innovation programme (project EpiPose to WJE).

Publisher Copyright:
© 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license

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