Tracking the Dynamics and Allocating Tests for COVID-19 in Real-Time: an Acceleration Index with an Application to French Age Groups and Départements^*

Abstract

An acceleration index is proposed as a novel indicator to track the dynamics of the COVID-19 in real-time. Using French data on cases and tests for the period following the first lock-down - from May 13, 2020, onwards - our acceleration index shows that the ongoing pandemic resurgence can be dated to begin around July 7. It uncovers that the pandemic acceleration has been stronger than national average for the [59-68] and [69-78] age groups since early September, the latter being associated with the strongest acceleration index, as of October 25. In contrast, acceleration among the [19-28] age group is the lowest and is about half that of the [69-78], as of October 25. In addition, we propose an algorithm to allocate tests among French departments, based on both the acceleration index and the feedback effect of testing. Our acceleration-based allocation differs from the actual distribution over French territories, which is population-based. We argue that both our acceleration index and our allocation algorithm are useful tools to guide public health policies as France enters a second lock-down period with indeterminate duration.

An Early Assessment of Curfew and Second COVID-19 Lock-down on Virus Propagation in France

“…The copyright holder for this this version posted November 13, 2020. ; https://doi.org/10.1101/2020.11.11.20230243 doi: medRxiv preprint Figure 4: Acceleration index for French départements in different treatment groups (Lock-down only, curfew 2+ for second week of curfew followed by lock-down, curfew 1+ for two weeks of curfew followed by lock-down) for both age groups (weekly averages for the 3 consecutive weeks also shown in Figure 1). Dashed horizontal line in right panel represents when acceleration index equals 1. in Baunez et al [1], more positive cases are not necessarily equivalent to greater acceleration. It may therefore be asked whether the governmental selection criteria were the right ones in the first place.…”

“…It is therefore difficult to judge unambiguously which of the policy measures was the most effective one, other than to say that lock-down measures have a quicker impact on the whole population, but very possibly with much higher economic and social costs than curfew measures. Given that the population aged 60 and more is notoriously more at risk of severe COVID-19 consequences, our data analysis may 1 A caveat is in order to indicate that the eight métropoles are not exactly corresponding to the départements in which they are. However, in the following, we consider métropoles to correspond to départements and therefore refer to 16 départements for the first curfew, one for each of the eight métropoles and the eight départements to which corresponds "Île de France".…”

An Early Assessment of Curfew and Second COVID-19 Lock-Down on Virus Propagation in France

“…As stressed in Baunez et al [1], accurate information about the dynamics of a pandemic rests on both the number of cases and the number of tests, and that the former cannot be properly understood without the latter. In the aforementioned paper, we address this pressing issue and provide an acceleration index that relates to the daily and average positivity rates, in the following way.…”

“…First, from October 17 onwards, eight major cities and their adjacent surroundings called "métropoles", plus the whole of "Île de France" which includes Paris, all together corresponding to 16 "départements" (roughly counties) were put under curfew from 9pm to 6am. 1 The following week, 38 départements were further added, so that a total of 54 out of 96 départements of metropolitan France were declared under mandatory curfew from October 23 onwards. Finally, starting on October 30, a nation-wide lock-down was implemented and is still ongoing.…”

“…To make this assessment, we update the acceleration index introduced in Baunez et al [1]. This index tracks in real-time the propagation of COVID-19 and can do so at very granular levels.…”