Working Paper: CEPR ID: DP15494
Authors: Thiemo Fetzer; Thomas Graeber
Abstract: Contact tracing has been a central pillar of the public health response to the COVID-19 pandemic. Yet, contact tracing measures face substantive challenges in practice and well-identified evidence about their effectiveness remains scarce. This paper exploits quasi-random variation in COVID-19 contact tracing. Between September 25 and October 2, 2020, a total of 15,841 COVID-19 cases in England (around 15 to 20% of all cases) were not immediately referred to the contact tracing system due to a data processing error. Case information was truncated from an Excel spreadsheet after the row limit had been reached, which was discovered on October 3. There is substantial variation in the degree to which different parts of England areas were exposed -- by chance -- to delayed referrals of COVID-19 cases to to the contact tracing system. We show that more affected areas subsequently experienced a drastic rise in new COVID-19 infections and deaths alongside an increase in the positivity rate and the number of test performed, as well as a decline in the performance of the contact tracing system. Conservative estimates suggest that the failure of timely contact tracing due to the data glitch is associated with more than 125,000 additional infections and over 1,500 additional COVID-19-related deaths. Our findings provide strong quasi-experimental evidence for the effectiveness of contact tracing.
Keywords: Health; Coronavirus
JEL Codes: I31; Z18
Edges that are evidenced by causal inference methods are in orange, and the rest are in light blue.
| Cause | Effect |
|---|---|
| delayed referrals to contact tracing (I14) | increase in new COVID-19 infections (I14) |
| delayed referrals to contact tracing (I14) | increase in COVID-19-related deaths (I12) |
| each additional late referral to contact tracing (C41) | additional COVID-19 infections (Y50) |
| delayed referrals to contact tracing (I14) | total additional infections (I12) |
| late referrals to contact tracing (C34) | increase in daily death rate (J11) |