The COVID-19 pandemic is one of the greatest and most serious issues of our times, requiring several approaches to deal with it successfully and effectively. Consequently, it is very important to understand the biological mechanisms of virus propagation, as well as the governing diffusion dynamics. These dynamics can be studied using the notion of universality, according to which different systems or classes of systems can demonstrate the same dynamic behavior and dynamical features, regardless of underlying mechanisms and dynamic details.
Along these lines, a group of researchers from the University of West Attica - UNIWA, a UNAI member institution in Greece, jointly with researchers from the International Hellenic University, Aristotle University of Thessaloniki, and the University of Balearic Islands, came up with a new epidemiological model based on self-organized criticality (SOC). The value of this research is highlighted given the worldwide debate on issues such as the effectiveness of vaccination, social distancing, protective measures, and even the so-called ‘herd immunity’ approach.
A model simulating the dynamics of viral epidemic spread over a population based on self-organizing diffusion over a lattice, has been presented by the research team mentioned above. The proposed ‘Self Organizing Diffusion Model’ (SODM) treats the state of epidemic spread as a self-organizing system, a rather common procedure in nature, demonstrating the same dynamic behavior with an epidemic and it is capable of distinguishing viruses based on their aggression. This self-organizing feature originates from the complexity demonstrated by the system itself.
Verification of the model’s validity comes from the fitting of the model on epidemiological data concerning a given population. This SODM demonstrates a critical behavior within the theory of critical phenomena. Based on the principle of universality, it is expected that the current COVID-19 pandemic would follow the model’s dynamics. As a result, for this pandemic getting close to the critical point, as defined by the model, means that the time from peak to elimination becomes very long, and the number of infected population high.
When the system is released without any restrictions (the 'herd immunity' approach) the epidemic spread is smooth and its duration short, only if the virus has no characteristics of increased aggression. Otherwise, in the case of aggressive viruses, the system can be driven into uncontrolled situations in terms of high percentage of active, infected population, and most importantly in terms of an extended duration of the epidemic. The latter is a consequence of the system’s nonlinearity and its behavior within the frame of the theory of critical phenomena.
The study focuses on aggressive viruses such as SARS-CoV-2. For Dr. Yiannis Contoyiannis, from the UNIWA, “in such cases the 'herd immunity' approach leads directly to an extensive and prolonged spread of the epidemic, a pandemic, in fact.” As Prof. Pericles Papadopoulos says, “the only way to control this is social distancing and limiting physical contacts.” “These together with a most important factor, vaccination, are proved to set the control parameter of the system away from its critical value; thus, allowing a safe, virus-reduced environment,” the expert adds.
According to Prof. Stelios M. Potirakis, the proposed model allows “to assess the effectiveness of restrictive measures as these are combined with vaccination, providing a useful tool for decision-making.” The critical conclusion from the proposed model is the fact that the COVID-19 pandemic behaves like a physical phenomenon, and it can be studied from the angle of physics of critical phenomena. This is also an example of how universities advance the Sustainable Development Goal 3: Good Health and Well-Being, in these challenging times.