Modeling of Transformations during the Formation of Local Waves of SARS-CoV-2 Spreading at the Endemic Stage of the Pandemic

Abstract

Most of the predictions made by the author at the end of 2022 about the development of scenarios for the coronavirus epidemic at the beginning of 2024 have been confirmed. There is a fungible set of changing SARS-CoV-2 strains, among which there is no longer a leader. In Asian countries, in December 2023, regional outbreaks of morbidity due to strains from a new branch of Omicron, BA.2.86, began, just like a year ago, although, in the summer between waves, the incidence of COVID-19 was low. The predicted nonlocal COVID outbreak is a positive feedback loop: the more infections, the higher the likelihood of further mutations in the virus and the greater chances of strains evading antibodies. It has been confirmed by a number of studies that repeated COVID often causes long-term and severe immunosuppression. The factor of post-COVID immunodeficiency and T-cell depletion in susceptible groups maintains a reservoir for the accumulation of SARS-CoV-2 mutations. This specific phenomenon was not taken into account in model predictions a year ago. The concept of the SIRS model is not applicable to SARS-CoV-2. Omicron’s many branches make it difficult to create a new vaccine. Antigenic drift makes it possible to bypass vaccine immunity, but global outbreaks are not observed for a long time due to the persistence of cytotoxic CD8+ T cells in us. From a dynamic point of view, the COVID-19 pandemic is divided into clusters of regional epidemics and demonstrates oscillatory dynamics. The oscillations have changed their character, with the wave crests becoming longer, although smaller in amplitude. Epidemic waves do not develop so rapidly, but grow gradually; however, this only increases the final number of cases. The damped amplitude of the waves of infection that formed after the initial outbreak again turns into an extreme peak. This may be due to effects after crisis events: mass infections or an increase in virulence of a new strain that evades the antibodies of vaccine immunity, but is destroyable. The two situations are different. We classified the observed local epidemic scenarios of COVID waves according to the types of oscillations from a physical point of view. COVID waves are no longer classic decaying relaxation oscillations. Using simulation modeling, we analyzed variants of epidemic dynamics with sharp changes. Special epidemic scenarios of the sudden occurrence of a short wave as a probable development of the current situation in 2024 were studied on the basis of nonlinear equations with a deviating argument. The COVID wave of the JN.1 strain in winter 2024 is the second fastest growing in cases of severe disease after the Omicron BA.1 wave in spring 2022 and will inevitably lead to a new impulse round in the evolution of the coronavirus.