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 the viral spread. For any TTI strategy, however, a major challenge arises from pre- and asymptomatic transmission as well as TTI-avoiders, which contribute to hidden , unnoticed infection chains. In our semi-analytical model, we identified two distinct tipping points between controlled and uncontrolled spreading: one, at which the behavior-driven reproduction number of the hidden infections becomes too large to be compensated by the available TTI capabilities, and one at which the number of new infections starts to exceed the tracing capacity , causing a self-accelerating spread. We investigated how these tipping points depend on realistic limitations like limited cooperativity , missing contacts, and imperfect isolation , finding that TTI is likely not sufficient to contain the natural spread of SARS-CoV-2 . Therefore, complementary measures like reduced physical contacts and improved hygiene probably remain necessary.
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.
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