The complex processes governing an infectious disease remain an incomplete but significant area in systems medicine. Problems on the emerging dynamics at the interface of viral replication and transmission motivate the analysis of multiscale models, especially from a mathematical standpoint. A coupled system, which comprises ordinary differential equations, links within- and between-host scales by means of disease-induced transmission. Bifurcation analysis captures the dynamical relationship between the two scales by evaluating the predicted epidemic size as a function of viral replication. The analysis further suggests that conflicts can arise between effective vaccination and outbreak prevention.