Digital herd immunity and COVID-19

Vir B. Bulchandani, Saumya Shivam, Sanjay Moudgalya, S. L. Sondhi

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


A population can be immune to epidemics even if not all of its individual members are immune to the disease, so long as sufficiently many are immune - this is the traditional notion of herd immunity. In the smartphone era a population can be immune to epidemics even if not a single one of its members is immune to the disease - a notion we call 'digital herd immunity', which is similarly an emergent characteristic of the population. This immunity arises because contact-tracing protocols based on smartphone capabilities can lead to highly efficient quarantining of infected population members and thus the extinguishing of nascent epidemics. When the disease characteristics are favorable and smartphone usage is high enough, the population is in this immune phase. As usage decreases there is a novel 'contact-tracing phase transition' to an epidemic phase. We present and study a simple branching-process model for COVID-19 and show that digital immunity is possible regardless of the proportion of non-symptomatic transmission.

Original languageEnglish (US)
Article number045004
JournalPhysical Biology
Issue number4
StatePublished - Jul 2021

All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Biophysics
  • Structural Biology
  • Cell Biology


  • COVID-19
  • contact tracing
  • digital herd immunity


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