Why did the COVID-19 Epidemic Stop in China and does not Stop in the Rest of the World? (Application of the Two-Component Model)

The vastly different courses of the COVID-19 epidemic in China and the rest of the world are investigated and explained within two-component epidemic model. The model is based on separate accounting for the contribution to the epidemic from two types of immune response to a viral infection - innate and adaptive immunity. Any infected person becomes asymptomatic with probability (1−𝑝) or symptomatic with probability 𝑝. In the first case, innate immunity is sufficient to protect a person. In the second case, innate immunity is insufficient, and adaptive immunity comes into play. In the asymptomatic state, the person remains outwardly healthy, mobile and can spread the infection. In the symptomatic state, the person becomes ill, isolated and cannot spread the infection. We assume that the contribution to the epidemic process from asymptomatic carriers is dominant in comparison with the contribution from the usual incubation period in the symptomatic state. The key parameters of the model are the virus lifetime 𝑇 in the asymptomatic state and the spread rate 𝛽. At moderate 𝛽𝑇 values, the model describes a long, slowly decreasing morbidity plateau, which transforms into wave-like solution at 𝛽𝑇. In the case of 𝛽𝑇→∞, which corresponds to a stable non-pathogenic strain, the model solution is limited to single wave only. We believe that the spread of such a non-pathogenic strain and its subsequent dominance is responsible for ending the epidemic after the single wave of incidence in China. A way to stop the epidemic in the rest of the world may consist in displacing the circulating pathogenic virus with its stable non-pathogenic strain. Doi: 10.28991/SciMedJ-2021-0302-2 Full Text: PDF