Persistent heterogeneity not short-term overdispersion determines herd immunity to COVID-19

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Abstract

It has become increasingly clear that the COVID-19 epidemic is characterized by overdispersion whereby the majority of the transmission is driven by a minority of infected individuals. Such a strong departure from the homogeneity assumptions of the traditional well-mixed compartment model is usually hypothesized to be the result of short-term super-spreader events, such as an individual’s extreme rate of virus shedding at the peak of infectivity while attending a large gathering without appropriate mitigation. However, we demonstrate that the spread of epidemics is primarily sensitive to longterm, or persistent heterogeneity of individual susceptibility or infectivity. We demonstrate how to incorporate this heterogeneity into a wide class of epidemiological models, and derive a non-linear dependence of the effective reproduction number R e on the susceptible population fraction S . Persistent heterogeneity has three important consequences compared to the effects of short-term overdispersion: (1) It results in a major modification of the early epidemic dynamics; (2) It significantly suppresses the herd immunity threshold; (3) It also significantly reduces the final size of the epidemic. We estimate social and biological contributions to persistent heterogeneity using data on real-life face-to-face contact networks and age variation of the incidence rate during the COVID-19 epidemic. In addition, empirical data from the COVID-19 epidemic in New York City (NYC) and Chicago, as well as 50 US states provide a consistent characterization of the level of heterogeneity. Our estimates suggest that the hardest-hit areas, such as NYC, are close to the heterogeneity-modified herd immunity threshold following the first wave of the epidemic. However, this type of immunity is fragile as it wanes over time if the pattern of social interactions changes substantially .

This study demonstrates how a wide class of epidemiological models can be adapted for applications to heterogeneous populations in the context of the COVID-19 epidemic. It is shown that a persistent heterogeneity, rather than bursty short-term variations in infection transmission is responsible for self-limiting epidemic dynamics. Compact generalizations of the classical results for the herd immunity threshold and the final size of an epidemic are derived. The degree of persistent heterogeneity is estimated from data on real-life face-to-face contact networks, and on age variation of susceptibility to COVID-19. The estimate is further supported by the analysis of the empirical data from the epidemic in NYC and Chicago, as well as in 50 US states. The results suggest that by the end of the first wave of the epidemic, the hardest-hit areas, such as NYC, have been close to the heterogeneity-modified herd immunity, thereby limiting their vulnerability to a potential second wave of the epidemic.

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  1. SciScore for 10.1101/2020.07.26.20162420: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board Statementnot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    No key resources detected.


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    About SciScore

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  2. SciScore for 10.1101/2020.07.26.20162420: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    This work made use of the Illinois Campus Cluster, a computing resource that is operated by the Illinois Campus Cluster Program (ICCP) in conjunction with the National Center for Supercomputing Applications (NCSA) and which is supported by funds from the University of Illinois at Urbana-Champaign.
    Campus Cluster Program
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    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore is not a substitute for expert review. SciScore checks for the presence and correctness of RRIDs (research resource identifiers) in the manuscript, and detects sentences that appear to be missing RRIDs. SciScore also checks to make sure that rigor criteria are addressed by authors. It does this by detecting sentences that discuss criteria such as blinding or power analysis. SciScore does not guarantee that the rigor criteria that it detects are appropriate for the particular study. Instead it assists authors, editors, and reviewers by drawing attention to sections of the manuscript that contain or should contain various rigor criteria and key resources. For details on the results shown here, including references cited, please follow this link.