Fundamental limitations of contact tracing for COVID-19

Contact tracing has played a central role in COVID-19 control in many jurisdictions and is often used in conjunction with other measures such as travel restrictions and social distancing mandates.

The authors explore various factors that can lead to contact tracing being ineffective, including delays in testing, calling contacts, and isolating.

Read this open access paper on the FACETS website.

They discuss how even under ideal circumstances, contact tracing that is initiated after a symptomatic individual tests positive for COVID-19 can only prevent a fraction of onward transmissions from contacts. This is because transmission happens early enough compared to symptoms that it is not feasible to notify contacts in time to prevent most onward transmission.

Contact tracing alone is insufficient to prevent exponential growth in the number of cases in a population with little immunity. Even when used effectively with other measures, occasional bursts in call loads can overwhelm contact tracing systems and lead to a loss of control.

To control the spread of COVID-19, contact tracing needs to be supplemented with other measures.

The authors propose embracing approaches to COVID-19 control that identify cases early, even without symptoms, in whatever way is economically feasible — either with fast and cheap tests that can be deployed widely, with pooled testing, or with screening of groups of individuals more likely to be infected.

These considerations are important both in regions where widespread vaccination has been deployed and in those where few residents have been immunized.

Read the paper — Fundamental limitations of contact tracing for COVID-19 by Paul Tupper, Sarah P. Otto, and Caroline Colijn.