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. Suppose once vaccinated, a person cannot catch a cold or give a cold to someone else. At the competitively determined output level, the marginal social benefit will be:

A) equal to P₀.
B) less than P₀.
C) greater than or less than P₀ depending on the income elasticity of demand and the effectiveness of the vaccine.
D) greater than P₀.