Abstract
To explain the prevalence of asymptomatic SARS-CoV-2 infection forms, a hypothesis on a single virus mutation that causes changes in two important factors such as virus infectiousness and pathogenicity is proposed. According to this hypothesis, susceptible and asymptomatic forms affect the rate of change in infectiousness and pathogenicity, thereby influencing the rate of infectivity and the onset of a disease and as a result, altering the ratio of asymptomatic forms to symptomatic cases. With a mathematical model, constructed based on this hypothesis and identified using data from the first wave of COVID-19 in Saint-Petersburg, a correlation between changes in microbiological parameters of the model and changes in a ratio of asymptomatic forms to symptomatic cases is verified. It is concluded that single virus mutation may affect the ratio.