The challenges of containing SARS-CoV-2 via test-trace-and-isolate

TL;DR

This paper analyzes the limitations of test-trace-and-isolate strategies for containing SARS-CoV-2, highlighting the conditions under which they fail and emphasizing the need for additional measures.

Contribution

It introduces a semi-analytical model identifying critical tipping points that lead to uncontrolled spread despite TTI efforts.

Findings

Two critical thresholds trigger uncontrolled spread.

TTI alone is insufficient without additional measures.

Factors like cooperation and contact tracing capacity significantly impact containment.

Abstract

Without a cure, vaccine, or proven long-term immunity against SARS-CoV-2, test-trace-and-isolate (TTI) strategies present a promising tool to contain its spread. For any TTI strategy, however, mitigation is challenged by pre- and asymptomatic transmission, TTI-avoiders, and undetected spreaders, who strongly contribute to hidden infection chains. Here, we studied a semi-analytical model and identified two tipping points between controlled and uncontrolled spread: (1) the behavior-driven reproduction number of the hidden chains becomes too large to be compensated by the TTI capabilities, and (2) the number of new infections exceeds the tracing capacity. Both trigger a self-accelerating spread. We investigated how these tipping points depend on challenges like limited cooperation, missing contacts, and imperfect isolation. Our model results suggest that TTI alone is insufficient to contain an otherwise unhindered spread of SARS-CoV-2, implying that complementary measures like social distancing and improved hygiene remain necessary.