The X-axis represents the Quantity of ColdVax (units). The Y-axis represents the Price ($). The supply curve (S) represents the marginal private cost (MPC) of producing ColdVax. It shows the additional cost incurred by producers for each unit of the vaccine they make. The demand curve (D) represents the marginal private benefit (MPB) to consumers. It shows how much consumers are willing to pay for each unit of ColdVax based on the direct benefit they receive (reduced risk of getting sick). The marginal social benefit (MSB) curve lies above the demand curve (D) and represents ColdVax's overall societal benefit. It incorporates both the direct benefit to vaccinated individuals (reflected in D) and the indirect benefit to society from reduced illness transmission (the positive externality). This graph illustrates how there's a gap between the marginal private benefit (D) and the marginal social benefit (MSB) due to the positive externality associated with vaccination