Answer: demand curve for vapes shifts to the left.
Explanation:
Based on the information given in the question, since the celebrity starts an ad campaign talking about the dangers of vaping, this will lead to a leftward shift in the demand curve.
When the demand curve shifts to the left, it simply means that there'll be a reduction in the number of vapes that people will buy. There'll be a reduction in the demand due to the dangers associated with vapes.