[IMS Seminar] Universal properties of Covid-19 diffusion in the population and effects of the pandemic on the excess mortality

ON2022-09-05TAG: ShanghaiTech UniversityCATEGORY: Lecture

Date: September 8, Thursday, 11:00-12:00

Location: RS408 at IMS; Tecent Meeting: 998-418-636

Online Link: http://video.ims.shanghaitech.edu.cn/#/onlines/7

Speaker: Michael Levitt, Department of Structural Biology, Stanford University; Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University

Michael Levitt is the Robert W. and Vivian K. Cahill Professor of structural biology at Stanford University. He received the 2013 Nobel Prize in Chemistry, together with Martin Karplus and Arieh Warshel, for the development of multiscale models for complex  chemical systems. Levitt was elected a Fellow of the Royal Society in 2001, and a member of the National Academy of Sciences in 2002.
Since 2018, Michael Levitt has been a Distinguished Professor-in-Residence at SIAIS, ShanghaiTech University. 

A pipeline involving data acquisition, curation, graphing and mathematical models of early Covid-19 outbreaks worldwide, shows that the total number of cases or deaths never grows exponentially. Instead, the exponential growth rate (; X(t) is the total number of cases at day t) decreases linearly on a log scale, which indicates Gompertz growth. Moreover, multiple outbreaks happening in the same location can be accurately fitted by a sum of Gompertz functions starting at different times. This property appears to be universal and independent of the size of the affected location.  Simulations of the virus propagation in networks of different topologies show that we can reproduce the Gompertz growth of Covid-19 by modeling social interaction as a scale free network, i.e. a network in which nodes with many more neighbors than average are relatively common.  Those high connectivity nodes are infected early in the outbreak and spread the infection very rapidly.  As these nodes are no longer able to infect their neighbors, the rate of spread slows down immediately.  Geometrically this is seen in that the “surface” of the epidemic, the number of susceptible nodes in contact with the infected nodes, decreases exponentially with time. The speed and impact of the epidemic depend on only three microscopic parameters (the average number of contacts each node makes, the probability of being infected by a neighbor and the probability of recovery) and can be linked to macroscopic parameters such as the time constant of the infection propagation and the total number of infected cases at the plateu.

Finally, we analyzed the impact of the pandemics in term of excess deaths in 33 high-income countries for which data were available in the Human Mortality Database (HMD at mortality.org). We computed the number of excess deaths with and without adjusting for age and the ratio R of excess deaths over recorded COVID-19 deaths. In our analyses, after age-adjustment, 8 of 33 countries had no overall excess deaths; there was a death deficit in children; and 0.478 million (29.7%) of the excess deaths were in people <65 years old. The R values’ range exceeded 0.3 in all 33 countries and in 16 of them R exceeded 1. Our analysis indicates that after adjusting for age, excess deaths may be lower than previously calculated.