How human behavior drives the balance of symptomatic and asymptomatic cases in emerging infections

Human behavioral changes in response to observing disease in others play a crucial role in the spread of epidemics. These behaviors create selective pressures that influence a virus's ability to survive. This study explores how human behavioral adaptations influence the co-evolution of symptomatic and asymptomatic pathogen strains during an epidemic. Using a deterministic Susceptible-Infectious-Removed (SIR) model, it examines the role of spontaneous social distancing (SD) in shaping the selection pressures on these strains. The analysis highlights how behavioral changes can drive shifts in the prevalence of symptomatic versus asymptomatic cases, offering insights into the evolutionary dynamics of pathogen variants. Individuals initiate SD after contact with symptomatic cases, either by reducing interactions with everyone or by specifically avoiding symptomatic individuals. The analysis shows that homogeneous contact reduction tends to favor symptomatic strain, while targeted avoidance of symptomatic cases promotes the selection of asymptomatic one. The study underscores the complex, non-linear dynamics of selections under different levels of social distancing. A global sensitivity analysis highlights the significance of behavioral parameters in controlling the overall size of the infection. The findings emphasize the need for public health strategies that account for human behavior to effectively limit the spread and evolution of viral strains.