Refer to the Graph Shown, Which Shows the Demand and Supply

Refer to the graph shown, which shows the demand and supply for a new vaccine against the common cold. Once vaccinated, a person cannot catch a cold or give a cold to someone else. The socially efficient level of output is:

A) less than Q₀.
B) greater than or less than Q₀ depending on the income elasticity of demand and the effectiveness of the vaccine.
C) greater than Q₀.
D) equal to Q₀.