Epidemic Contact Tracing — Backward & Forward Network

SIR epidemic on a network with contact tracing. Backward tracing finds the source; forward tracing quarantines exposed contacts.

Parameters

S: — I: — R: — Q: —
Susceptible
Infected
Recovered
Quarantined
Backward tracing (Endo et al. 2020): trace who infected the detected case — finds superspreaders upstream. Forward tracing: isolate contacts exposed by a case — cuts downstream chains. Combined tracing is dramatically more effective than forward-only, especially for R₀ > 1.