Digital Herd Immunity and COVID-19

Vir Bannerjee Bulchandani; Saumya Shivam; Sanjay Moudgalya; S L Sondhi

Our second contribution is to frame the overall discussion in a language more familiar to physicists and students of complex phenomena more generally-that of phases, phase transitions and emergent properties. The bottom line here is the idea that the immunity of a population to epidemic growth is an emergent, or collective, property of the population. For traditional vaccination or epidemic-induced "herd immunity", this feature gets conflated with the fact that individuals can be immune to the disease at issue. But mass digital contact tracing now makes it possible for the population to be immune to epidemic growth even as no individual has immunity to the underlying disease. We propose to refer to this as the existence of a "digital herd immunity". This fits well into the general idea of an emergent property, which does not exist at the level of the microscopic constituents but exists for the collective [13, 14] . We would be remiss if we did not note that epidemiologists have previously referred to this state of affairs as "herd protection" and "sustained epidemic control" [5] . Our intention with the proposed terminology is both to frame a public health goal by including the word digital and to emphasize the emergent nature of a herd immunity.