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Phase portraits in the proportion of susceptible and carrier (
–
) and susceptible and infective (
–
) planes for varying values of the basic reproduction number 
and 
. The trajectories illustrate convergence toward a unique endemic equilibrium. For 
, the system exhibits damped oscillatory behavior before settling at equilibrium, whereas for 
, convergence occurs with minimal oscillations, indicating a stronger attracting endemic state as transmission intensity increases
