lancet-header

Preprints with The Lancet is part of SSRN´s First Look, a place where journals identify content of interest prior to publication. Authors have opted in at submission to The Lancet family of journals to post their preprints on Preprints with The Lancet. The usual SSRN checks and a Lancet-specific check for appropriateness and transparency have been applied. Preprints available here are not Lancet publications or necessarily under review with a Lancet journal. These preprints are early stage research papers that have not been peer-reviewed. The findings should not be used for clinical or public health decision making and should not be presented to a lay audience without highlighting that they are preliminary and have not been peer-reviewed. For more information on this collaboration, see the comments published in The Lancet about the trial period, and our decision to make this a permanent offering, or visit The Lancet´s FAQ page, and for any feedback please contact preprints@lancet.com.

Relative Role of Border Restrictions, Case Finding and Contact Tracing in Controlling SARS-CoV-2 in the Presence of Undetected Transmission

22 Pages Posted: 17 May 2021

See all articles by Rachael Pung

Rachael Pung

Government of the Republic of Singapore - Communicable Diseases Division

Hannah E. Clapham

National University of Singapore (NUS) - Saw Swee Hock School of Public Health

Vernon J. Lee

Ministry of Health, Singapore; National University of Singapore (NUS) - Saw Swee Hock School of Public Health

Adam J. Kucharski

London School of Hygiene & Tropical Medicine - Centre for Mathematical Modelling of Infectious Diseases

More...

Abstract

Background: Several countries have controlled the spread of COVID-19 through varying combinations of border restrictions, case finding, contact tracing and careful calibration on the resumption of domestic activities. However, evaluating the effectiveness of these measures based on observed cases alone is challenging as it does not reflect the transmission dynamics of missed infections. 

Methods: Combining data on notified local COVID-19 cases with known and unknown sources of infections (i.e. linked and unlinked cases) in Singapore in 2020 with a transmission model, we reconstructed the incidence of missed infections and estimated the relative effectiveness of different types of outbreak control. We also examined implications for estimation of key real-time metrics — the reproduction number and ratio of unlinked to linked cases, using observed data only as compared to accounting for missed infections.

Findings:  Prior to the partial lockdown in Singapore, initiated in April 2020, we estimated 89% (95%CI 75–99%) of the infections caused by notified cases were contact traced, but only 12.5% (95%CI 2–69%) of the infections caused by missed infectors were identified. We estimated that the reproduction number was 1.23 (95%CI 0.98–1.54) after accounting for missed infections but was 0.90 (95%CI 0.79-1.1) based on notified cases alone. At the height of the outbreak, the ratio of missed to notified infections was 34.1 (95%CI 26.0–46.6) but the ratio of unlinked to linked infections was 0.81 (95%CI 0.59–1.36). Our results suggest that when case finding and contact tracing identifies at least 50% and 20% of the infections caused by missed and notified cases respectively, the reproduction number could be reduced by more than 14%, rising to 20% when contact tracing is 80% effective. 

Interpretation: Depending on the relative effectiveness of border restrictions, case finding and contact tracing, unobserved outbreak dynamics can vary greatly. Commonly used metrics to evaluate outbreak control — typically based on notified data — could therefore misrepresent the true underlying outbreak. 

Funding: Ministry of Health, Singapore.

Declaration of Interests: None to declare.

Suggested Citation

Pung, Rachael and Clapham, Hannah E. and Lee, Vernon J. and Kucharski, Adam J., Relative Role of Border Restrictions, Case Finding and Contact Tracing in Controlling SARS-CoV-2 in the Presence of Undetected Transmission. Available at SSRN: https://ssrn.com/abstract=3844817 or http://dx.doi.org/10.2139/ssrn.3844817

Rachael Pung (Contact Author)

Government of the Republic of Singapore - Communicable Diseases Division ( email )

12 College Road
169852
Singapore

Hannah E. Clapham

National University of Singapore (NUS) - Saw Swee Hock School of Public Health ( email )

16 Medical Drive
#10-01
117597
Singapore

Vernon J. Lee

Ministry of Health, Singapore ( email )

Singapore

National University of Singapore (NUS) - Saw Swee Hock School of Public Health ( email )

16 Medical Drive
#10-01
117597
Singapore

Adam J. Kucharski

London School of Hygiene & Tropical Medicine - Centre for Mathematical Modelling of Infectious Diseases

London
United Kingdom