Early detection of variants of concern via funnel plots of regional reproduction numbers

Abstract

Tools to early detect the emergence of a new variant of concern are essential to develop strategies that contain epidemic outbreaks and their health-economic-social consequences. For example, knowing in which region a variant of concern appears or starts spreading enables prompt actions to circumscribe the diffusion area. This paper presents ‘funnel plots’ as a statistical method that can quickly identify regions of a country where the reproduction number is anomalous with respect to the national one, thus triggering cross-cutting research, while keeping false alarms under control. COVID-19 data demonstrate the efficacy of the method in the early detection of Delta and Omicron variants in India, South Africa, England, and Italy, as well as a malfunctioning episode of the diagnostic infrastructure in England.