When Externalities Collide: Influenza and Pollution

Influenza and air pollution each pose significant public health risks with large global economic consequences. The common pathways through which harms presents an interesting case of compounding risk via interacting externalities. Using instrumental variables based on changing wind directions, we show increased levels contemporaneous significantly increase influenza hospitalizations. We exploit random variations in the effectiveness vaccine as additional instrument to protection neutralizes this relationship. This suggests seemingly disparate policy actions control vaccination campaigns jointly provide greater returns than those implied by addressing either isolation.