Science and Medicine

Covid-19: math helps stem the virus

28 August 2020 | Written by La redazione

Published in "Nature Communications" the study by the University of Padua that allows you to know how to measure the daily isolation effort to keep the epidemic under control and to know the number of infected subjects (even asymptomatic)

The group of researchers of Professor Andrea Rinaldo of the Universities of Padua, Ca ‘Foscari Venice, Politecnico di Milano and Ecole Polytechnique Fédérale Lausanne (EPFL) modeled the course of the coronavirus pandemic in Italy taking into account the progression and subsequent relaxation of the measures restrictive arranged to contain the transmission of infections. The model allows, in particular, to calculate the number of infected (including asymptomatic infected which are a fundamental source of transmission of infections) and calculates the daily isolation effort necessary to keep the epidemic curve on a decreasing trajectory.

Previous studies. In April 2020 with a publication entitled “Spread and dynamics of the COVID-19 epidemic in Italy: Effects of emergency containment measures” on “PNAS”, the research group of Andrea Rinaldo, Professor of Hydraulic Construction at the University and Director of Laboratory of Ecohydrologie (ECHO) at EPFL, had developed in detail a mathematical model on the development of the COVID-19 pandemic in Italy. Based on the number of deaths attributed to the coronavirus and their geographical distribution among 107 Italian provinces (the most precise level of detail available) as well as on mobility data obtained from the geolocation of mobile phones, the April model faithfully photographed the evolution of the pandemic.

The new study. In the publication in “Nature Communications” entitled “The geography of COVID-19 spread in Italy and implications for the relaxation of confinement measures”, by varying the basic parameters (mobility and transmission rates among others) it was possible to predict different scenarios of future propagation, especially before and after the restrictive measures.

“Since the creation of the first model we have continuously updated the calibrations, for example taking into account the effects of the release of the containment after 4 May – says Andrea Rinaldo, professor at the University of Padua -. We also made sure that the previously estimated values ​​of the pandemic trend were verified with extreme fidelity. We then calculated data impossible to obtain in the field. Our direct knowledge of the total number of people infected with the coronavirus is based on the number of tests performed, but this does not correspond to reality: there are in fact a large number of asymptomatics not confined to isolation and an objective source of contagion. Thanks to our model – explains Rinaldo – it is now possible to reliably estimate the key factors in the transmission of COVID-19 infections. If the estimate of the total number of infected people is up-to-date and reliable, the model can, in cascade, determine the daily isolation effort needed to keep the pandemic under control ».

The results and possible scenarios. In the article published today (but accepted over a month ago) the researchers of the team led by Andrea Rinaldo had already predicted that with the elimination of confinement the transmission speed would increase. And this is precisely what is observed today. The research group therefore evaluated various possible scenarios depending on the extent of the increase observed.

If the increase in the transmission rate were 40%, a resumption of infections would be observed in most of Italy. The researchers state that from the data developed by the model it emerges that 5.5% of infected individuals need to be isolated daily to remain below the 40% threshold – critical threshold – to keep the reproduction index below the units (decreasing epidemic trajectory). Keeping the epidemic curve on a downward trajectory is an important goal in containment policies because it avoids a new confinement and its deleterious effects on the country’s economy.

In Italy, cases of COVID-19 are currently on the rise. The state of emergency has been extended until 15 October and the use of the mask is mandatory in all closed places such as public transport and shops. “The increase in the number of confirmed infections and the much lower average age of the same are a cause of great concern for us – concludes Andrea Rinaldo -. As the cold season approaches, indoor activities will make airborne infections much more aggressive, unless strong discipline in personal protection is in place. In my opinion, the mask should remain mandatory until a vaccine is widely available ».

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