COVID-19 epidemic is characterized by the short-term overdispersion manifested in the phenomenon of super-spreading, whereby the majority of the transmission is driven by a minority of infected individuals. On the other hand, as demonstrated in this work, the eventual outcome of the epidemic is determined by the persistent heterogeneity of the population. While this long-term heterogeneity leads, e.g., to a reduction of the Herd Immunity Threshold (HIT), the overall progression of the epidemic is shaped by both persistent and short-term variations in individual susceptibilities and infectivities. We demonstrate how to incorporate persistent heterogeneity into a wide class of epidemiological models, and derive a non-linear dependence of the effective reproduction number Re on the susceptible population fraction S. This approach is further generalized to account for time variations in individual social activity. It is shown that the suppression of the early waves of the COVID-19 epidemic has been facilitated in some locations by Transient Collective Immunity (TCI). This is a fragile state that could be achieved below HIT, but would wane over time due to changing levels of individual social activity. Transient and long-term levels of heterogeneity are estimated by using empirical data from the COVID-19 epidemic as well as from real-life face-to-face contact networks. These results suggest that the hardest-hit areas, such as NYC, have achieved TCI following the first wave of the epidemic, but likely remain below the long-term HIT.
|Publisher||Cold Spring Harbor Laboratory Press|
- severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
- Novel coronavirus