https://doi.org/10.1140/epjp/s13360-020-00811-z
Regular Article
Chaos, percolation and the coronavirus spread: a two-step model
1
School of Physics and Information Technology, Shaanxi Normal University, 710119, Xi’an, China
2
Cyclotron Institute, Texas A&M University, 77843, College Station, TX, USA
3
Laboratori Nazionali del Sud, INFN, 95123, Catania, Italy
Received:
3
September
2020
Accepted:
25
September
2020
Published online:
9
October
2020
We discuss a two-step model for the rise and decay of a new coronavirus (Severe Acute Respiratory Syndrome-CoV-2) first reported in December 2019, COVID-19. The first stage is well described by the same equation for turbulent flows, population growth and chaotic maps: a small number of infected, 
, grows exponentially to a saturation value, 
. The typical growth time (aggressive spreading of the virus) is given by 
where 
is the Lyapunov exponent. After a time 
determined by social distancing and/or other measures, the spread decreases exponentially analogous to nuclear decays and non-chaotic maps. Some countries, like China, S. Korea and Italy, are in this second stage while others including the USA are near the end of the growth stage. The model predicted 15,000 (±2250) casualties for the Lombardy region (Italy) at the end of the spreading around May 10, 2020. Without the quarantine, the casualties would have been more than 50,000, one hundred days after the start of the pandemic. The data from the 50 US states are of very poor quality because of an extremely late and confused response to the pandemic, resulting unfortunately in a large number of casualties, more than 70,000 on May 6, 2020, and more than 170,000 on August 21, 2020. S. Korea, notwithstanding the high population density (
) and the closeness to China, responded best to the pandemic with 255 deceased as of May 6, 2020, and 301 on August 21, 2020.
© Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
