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 COVID-19 in real-time. Using data on cases and tests in France for the period between the first and second lock-downs—May 13 to October 25, 2020—our acceleration index shows that the pandemic resurgence can be dated to begin around July 7. It uncovers that the pandemic acceleration was stronger than national average for the [59–68] and especially the 69 and older 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 was the lowest and is about half that of the [69–78]. In addition, we propose an algorithm to allocate tests among French “départements” (roughly counties), 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 might possibly enter a third lock-down period with indeterminate duration.

COVID-19 Acceleration and Vaccine Status in France - Summer 2021

“…In Baunez et al [1], we have proposed a real-time indicator, the acceleration index, that measures whether the pandemic is accelerating or decelerating in a given population. The acceleration index is defined as the elasticity of cumulated positive cases to cumulated tests.…”

“…Disease Control and Prevention (CDC) indicates for example that fully vaccinated people with the Delta variant can spread the virus, although it appears for a shorter period of time. 1 It is therefore of great importance for any public health authority to be able to measure and understand correctly the viral spread, including among the vaccinated population.…”

Correcting the Reproduction Number for Time-Varying Tests: a Proposal and an Application to COVID-19 in France*

“…The main purpose of this section is to derive a theoretical relationship between both concepts, which helps both to explain why they are different, to give a sense of the magnitude of their difference, and to state the conditions under which they are equivalent. We then turn, in the next section, to data to gauge whether the difference between the two matters to track the COVID- 19 As stressed in Baunez et al [5], accurate information about the dynamics of a pandemic rests on both the number of cases and the number of tests, and the former cannot be properly understood without the latter. In that paper, we introduce an acceleration index, denoted ε T at date T , which is an elasticity that measures the proportional responsiveness of cases with respect to tests.…”

COVID-19 Acceleration and Vaccine Status in France - Summer 2021

“…A certain number of studies are starting to suggest that the Delta variant" [...] is believed to spread faster than other variants" (Planas et al 2021) and the US-based Centers for Disease Control and Prevention (CDC) indicates for example that fully vaccinated people with the Delta variant can spread the virus, although it appears for a shorter period of time. 1 It is therefore of great importance for any public health authority to be able to observe correctly the viral spread, including among the vaccinated population.…”

“…If the viral transmissions are low, but with a tendency to accelerate, vaccine campaigns alone will not be able to curb the pandemic. In Baunez et al [1] we propose an acceleration index, which is the percentage change in cases given a percentage change in tests. The intuition is that if we increase tests by, say, one percent and find more than one percent of cases, we infer that the pandemic is accelerating.…”