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Title: Where Externalities Collide: Influenza and Pollution

Abstract: Influenza and air pollution each pose significant public health risks with global economic consequences. The common pathways through which each harms health presents a case of compounding risk via interacting externalities. Using instrumental variables based on changing wind directions, we first show that increased levels of contemporaneous pollution increase influenza hospitalizations. We then exploit random variations in the effectiveness of the influenza vaccine as an additional instrument to show vaccine protection neutralizes this relationship. Evidence suggests seemingly disparate policy actions of pollution control and vaccination campaigns interact with each other, and pollution exposure gaps help explain racial gaps in influenza incidence.