A detailed study of the change in viral load for both low and higher levels of IFN production (q) is shown in Fig 5A and 5B, where the change of viral load (dV/dt in Eq 1) is decomposed into its four components (appearing on the right-hand side of Eq 1), whose relative contributions to the change in viral load vary by the stage of infection. The gene discussed is IFNA1; the disease is infection.