The "SIRV" model presents a familiar picture. Infections rise, while the susceptible population declines. Yet the green curve soon shows a distinct bend, indicating that the system is no longer being shaped by infection and recovery alone. The reason becomes clear as the vaccinated compartment is introduced. The purple trajectory represents individuals moving into the vaccinated state over time. As uptake increases, the susceptible pool is progressively reduced. That is precisely what accounts for the bend in the green curve. Once all compartments are considered together, the outbreak trajectory is visibly altered, with the epidemic wave moderated by the growing effect of vaccination.
