21.1 In Focus: The Impact and Mechanisms of Superspreading

Abstract

AbstractOne of the characteristic features of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is its tendency toward superspreading, where most onward transmission is linked to relatively few of those infected. Indeed, it has been shown that just around 10% of positive individuals account for 80% of new infections. The data necessary to quantify this superspreading tendency were available quite early, even before the outbreak was declared a pandemic. At the time, the epidemiological consequences of superspreading were not well understood, and mathematical models used for forecasting the pandemic trajectory were not equipped to incorporate this factor. More recently developed models have shown that such heterogeneity in transmission profoundly impacts the effects of mitigation measures, enhancing some strategies while rendering others less effective. This suggests that the overdispersion parameter k, roughly speaking “the estimated proportion of infected individuals responsible for 80% of the total secondary transmissions” (Endo et al. 2020), is a key statistical property of SARS-CoV-2 transmission, and that k should be rapidly quantified for any emerging pathogen, along with the basic reproductive number R0. While this research is still nascent, the overall picture is that the superspreading potential could be quantified in the early phase of a future pandemic and that this knowledge is a critical factor to inform the outbreak response.