An epidemiological model to manage post-lockdown scenarios of COVID-19

In Nature Communications, analysis of relationship between measures for identifying and isolating infected, and spread of virus


Although the COVID-19 pandemic is still heavily present in most countries throughout the world, and the necessary containment measures are being implemented globally, there is a strong debate about whether these measures can be partially relaxed, and if so, how and when.

In Italy, too, there is an increasingly urgent need to restart partially blocked socio-economic activities to control the spread of COVID-19. For this to be possible, reopening must be accompanied by effective monitoring and control methods that allow selective relaxing of containment measures without increasing the epidemic risk.

It is on these assumptions that, in recent months, the group of researchers who at the end of April had published an important study in the prestigious journal PNAS, further investigated and updated its analysis, reaching the conclusions recently published in Nature Communications. The team is composed of Professors Lorenzo Mari, Stefano Miccoli, Renato Casagrandi and Marino Gatto from the Politecnico di Milano; Enrico Bertuzzo and Damiano Pasetto from Ca' Foscari University in Venice; Andrea Rinaldo from the University of Padua and the EPFL in Lausanne.

The spatially explicit model used includes both the role of asymptomatic infections and mobility, and is able to estimate the expected development of the epidemic in different scenarios of containment measures (social distancing, personal protective equipment, limitation of mobility, identifying and isolating infected people). Moreover, having been developed based on data until mid-June, the model makes it possible to evaluate deviations from the epidemiological situation of that month (benchmark scenario) in case the resumption of many activities should lead to a recurrence of disease transmission. The effort required to detect and isolate infected people to prevent the reappearance of the epidemic is also estimated.

Considering that data from the last month confirms an increase in outbreaks and transmission of the virus, we estimate that an increase of, for example, 40% in the transmission rate can be counterbalanced by a control effort capable of isolating around 5.5% of exposed and highly infectious individuals on a daily basis, thus maintaining the epidemic curve on the benchmark trajectory.

explains Marino Gatto, professor of ecology at the Politecnico.

The study also made it possible to estimate the quota of asymptomatic infectious diseases and the total number of infected people in the different regions—figures confirmed by the coronavirus seroprevalence data in ISTAT statistics.

 

In the picture, the comparative analysis of data and model results for hospitalizations in 107 Italian provinces as of May 1, 2020.
a: a sketch of the Italian regions
b, c: the prevalence of cumulative hospitalizations in each Italian province up to May 1, reconstructed data (b) and model simulations (c)
d: ratio between the estimated transmission rate on May 1, and the one estimated at the beginning of the outbreak (February 24)

For more information:
Bertuzzo, E., Mari, L., Pasetto, D., Miccoli, S., Casagrandi, R., Gatto, M., Rinaldo A.
The geography of COVID-19 spread in Italy and implications for the relaxation of confinement measures.
Nat Commun 11, 4264 (2020).
The study online